diff --git a/modules/NIGHTDLL/nt_msg.c b/modules/NIGHTDLL/nt_msg.c
index 669f4c6..8226659 100644
--- a/modules/NIGHTDLL/nt_msg.c
+++ b/modules/NIGHTDLL/nt_msg.c
@@ -179,7 +179,7 @@ void ntmsg_newline() {
 	ntmsg_add(buf);
 }
 
-void ntmsg_add(char *msg) {
+void ntmsg_add(const char *msg) {
 	int len;
 	
 	SACT_DEBUG("len = %d\n", strlen(msg));
diff --git a/modules/NIGHTDLL/nt_msg.h b/modules/NIGHTDLL/nt_msg.h
index 6af9a32..6a28dd0 100644
--- a/modules/NIGHTDLL/nt_msg.h
+++ b/modules/NIGHTDLL/nt_msg.h
@@ -5,7 +5,7 @@ extern void ntmsg_init();
 extern void ntmsg_set_frame(int type);
 extern void ntmsg_set_place(int type);
 extern void ntmsg_newline();
-extern void ntmsg_add(char *msg);
+extern void ntmsg_add(const char *msg);
 extern int  ntmsg_ana(void);
 extern int  ntmsg_update(sprite_t *sp, MyRectangle *r);
 
diff --git a/modules/SACT/sprite.h b/modules/SACT/sprite.h
index 38e6102..a7b8341 100644
--- a/modules/SACT/sprite.h
+++ b/modules/SACT/sprite.h
@@ -83,7 +83,7 @@ extern void sp_draw_dmap(void* data, void* userdata);
 
 
 // in sprite_msg.c
-extern void smsg_add(char *msg);
+extern void smsg_add(const char *msg);
 extern void smsg_newline(int wNum, int size);
 extern void smsg_out(int wNum, int wSize, int wColorR, int wColorG, int wColorB, int wFont, int wSpeed, int wLineSpace, int wAlign, int wRSize, int wRFont, int wRLineSpace, int *wLength);
 extern void smsg_clear(int wNum);
diff --git a/modules/SACT/sprite_msg.c b/modules/SACT/sprite_msg.c
index f7bb7b5..05aaca4 100644
--- a/modules/SACT/sprite_msg.c
+++ b/modules/SACT/sprite_msg.c
@@ -188,7 +188,7 @@ static int setupmark(int wNum1, int wNum2, struct markinfo *minfo) {
     
   @param msg: 追加する文字列
 */
-void smsg_add(char *msg) {
+void smsg_add(const char *msg) {
 	int len;
 	
 	if (msg[0] == '\0') return;
diff --git a/modules/ShString/ShString.c b/modules/ShString/ShString.c
index 06e0495..6b6b7c5 100644
--- a/modules/ShString/ShString.c
+++ b/modules/ShString/ShString.c
@@ -45,8 +45,8 @@ static void ExchangeString(void) {
 	int target = getCaliValue();
 	int pat    = getCaliValue();
 	int patr   = getCaliValue();
-	char *start = v_str(target -1);
-	char *next;
+	const char *start = v_str(target -1);
+	const char *next;
 	char dst[STRVAR_LEN] = "";
 	
 	DEBUG_COMMAND("ShString.ExchangeString: %d,%d,%d:\n", target, pat, patr);
@@ -144,7 +144,7 @@ static void SetStringNum16(void) {
 	*/
 	int st = getCaliValue();
 	int *var = getCaliVariable();
-	char *str = v_str(st -1);
+	const char *str = v_str(st -1);
 	char _dst[100];
 	char *dst = _dst;
 	
diff --git a/src/ags.c b/src/ags.c
index 41a64a0..592723b 100644
--- a/src/ags.c
+++ b/src/ags.c
@@ -184,7 +184,7 @@ void ags_setViewArea(int x, int y, int width, int height) {
 	SetWindowSize(x, y, width, height);
 }
 
-void ags_setWindowTitle(char *src) {
+void ags_setWindowTitle(const char *src) {
 #define TITLEHEAD "XSystem35 Version "VERSION":"
 	BYTE *dst, *d;
 
@@ -396,7 +396,7 @@ void ags_delRegion(void *region) {
 	DelRegion(region);
 }
 
-int ags_drawString(int x, int y, char *src, int col) {
+int ags_drawString(int x, int y, const char *src, int col) {
 	int w;
 	
 	if (!check_param_xy(&x, &y)) return 0;
diff --git a/src/ags.h b/src/ags.h
index 496faf0..158513b 100644
--- a/src/ags.h
+++ b/src/ags.h
@@ -151,7 +151,7 @@ extern void ags_remove();
 /* ウィンド関係 */
 extern void ags_setWorldSize(int width, int height, int depth);
 extern void ags_setViewArea(int x, int y, int width, int height);
-extern void ags_setWindowTitle(char *str);
+extern void ags_setWindowTitle(const char *str);
 extern void ags_getDIBInfo(DispInfo *info);
 extern void ags_getWindowInfo(DispInfo *info);
 extern void ags_getViewAreaInfo(DispInfo *info);
@@ -194,7 +194,7 @@ extern void ags_putRegion(void *region, int x, int y);
 extern void ags_copyRegion(void *region, int sx, int sy, int w,int h,int dx,int dy);
 extern void ags_delRegion(void *region);
 
-extern int  ags_drawString(int x, int y, char *src, int col);
+extern int  ags_drawString(int x, int y, const char *src, int col);
 extern void ags_drawCg8bit(cgdata *cg, int x, int y); 
 extern void ags_drawCg16bit(cgdata *cg, int x, int y); 
 
diff --git a/src/font.h b/src/font.h
index 4eb2e7c..8b4ada4 100644
--- a/src/font.h
+++ b/src/font.h
@@ -46,13 +46,13 @@ struct _FONT {
 	
 	void (*sel_font)(int type, int size);
 	
-	struct agsurface *(*get_glyph)(unsigned char *str);
+	struct agsurface *(*get_glyph)(const unsigned char *str);
 	
-	int (*draw_glyph)(int x, int y, unsigned char *str, int col);
+	int (*draw_glyph)(int x, int y, const unsigned char *str, int col);
 	
 	boolean (*self_drawable)();
 	
-	int (*codeconv[FONTTYPEMAX])(unsigned char **msg);
+	int (*codeconv[FONTTYPEMAX])(const unsigned char **msg);
 };
 
 typedef struct _FONT FONT;
diff --git a/src/font_freetype2.c b/src/font_freetype2.c
index 26ce945..db94541 100644
--- a/src/font_freetype2.c
+++ b/src/font_freetype2.c
@@ -60,7 +60,7 @@ static FONT *this;
 static void pixmap2comimg(BYTE *src, int x, int y, int w, int h, int src_bpl);
 static void pixmapmono2comimg(BYTE *src, int x, int y, int w, int h, int src_bpl);
 
-static int toUnicode(unsigned char **msg) {
+static int toUnicode(const unsigned char **msg) {
 	int code;
 	
 	if (**msg >= 0xa0 && **msg <= 0xdf) {
@@ -74,7 +74,7 @@ static int toUnicode(unsigned char **msg) {
 	return code;
 }
 
-static int toSJIS(unsigned char **msg) {
+static int toSJIS(const unsigned char **msg) {
 	int code;
 
 	if (**msg >= 0xa0 && **msg <= 0xdf) {
@@ -88,7 +88,7 @@ static int toSJIS(unsigned char **msg) {
 	return code;
 }
 
-static int toSJIS0213(unsigned char **msg) {
+static int toSJIS0213(const unsigned char **msg) {
 	int code;
 	
 	if (**msg >= 0xa0 && **msg <= 0xdf) {
@@ -231,14 +231,14 @@ static void clear_canvas(void) {
 	memset(img_glyph.pixel, 0, GLYPH_PIXMAP_WIDTH * GLYPH_PIXMAP_HEIGHT);
 }
 
-static agsurface_t *font_ttf_get_glyph(unsigned char *_msg) {
+static agsurface_t *font_ttf_get_glyph(const unsigned char *_msg) {
 	FT_GlyphSlot   slot;
 	FT_UShort      code;
 	FT_Error       err;
 	FT_Pixel_Mode  pixelmode;
 	FT_Int         loadflag;
 	int x = 0;
-	unsigned char *msg = _msg;
+	const unsigned char *msg = _msg;
 	
 	if (fontset == NULL) return &img_glyph;
 	
@@ -300,7 +300,7 @@ static agsurface_t *font_ttf_get_glyph(unsigned char *_msg) {
 	return &img_glyph;
 }
 
-static int font_ttf_draw_glyph(int x, int y, unsigned char *str, int col) {
+static int font_ttf_draw_glyph(int x, int y, const unsigned char *str, int col) {
 	return 0;
 }
 
diff --git a/src/font_sdlttf.c b/src/font_sdlttf.c
index 0d3f6fd..2f6eb32 100644
--- a/src/font_sdlttf.c
+++ b/src/font_sdlttf.c
@@ -69,7 +69,7 @@ static void font_sdlttf_sel_font(int type, int size) {
 	}
 }
 
-static agsurface_t *font_sdlttf_get_glyph(unsigned char *msg) {
+static agsurface_t *font_sdlttf_get_glyph(const unsigned char *msg) {
 	static SDL_Surface *fs;
 	static agsurface_t result;
 
@@ -140,7 +140,7 @@ static void sdl_drawAntiAlias_8bpp(int dstx, int dsty, SDL_Surface *src, unsigne
 	SDL_UnlockSurface(sdl_dib);
 }
 
-static int font_sdlttf_draw_glyph(int x, int y, unsigned char *str, int cl) {
+static int font_sdlttf_draw_glyph(int x, int y, const unsigned char *str, int cl) {
 	SDL_Surface *fs;
 	SDL_Rect r_src, r_dst;
 	int w, h, maxy;
diff --git a/src/font_x11.c b/src/font_x11.c
index d47113f..5924594 100644
--- a/src/font_x11.c
+++ b/src/font_x11.c
@@ -151,7 +151,7 @@ static agsurface_t *get_drawn_glyph(const char *str, int w) {
 	return dst;
 }
 
-static agsurface_t *font_x11_get_glyph(unsigned char *str) {
+static agsurface_t *font_x11_get_glyph(const unsigned char *str) {
 	agsurface_t *dst;
 	int w;
 	BYTE *conv;
@@ -182,7 +182,7 @@ static agsurface_t *font_x11_get_glyph(unsigned char *str) {
 	return &img_glyph;
 }
 
-static int font_x11_draw_glyph(int x, int y, unsigned char *str, int col) {
+static int font_x11_draw_glyph(int x, int y, const unsigned char *str, int col) {
 	int w;
 	BYTE *conv;
 	
diff --git a/src/hankaku.c b/src/hankaku.c
index eb32af7..25dc59d 100644
--- a/src/hankaku.c
+++ b/src/hankaku.c
@@ -612,7 +612,7 @@ static BYTE hankakutable[3][192][2] = {{
 	{0x83, 0xff}
 }};
 
-BYTE *zen2han(BYTE *src) {
+BYTE *zen2han(const BYTE *src) {
 	BYTE c0, c1;
 	char *dst, *_dst;
 	
@@ -644,7 +644,7 @@ BYTE *zen2han(BYTE *src) {
 	return _dst;
 }
 
-BYTE *han2zen(BYTE *src) {
+BYTE *han2zen(const BYTE *src) {
 	BYTE c0;
 	BYTE *dst, *_dst;
 	BYTE *kindex;
diff --git a/src/message.c b/src/message.c
index 759b935..e02f3c5 100644
--- a/src/message.c
+++ b/src/message.c
@@ -58,7 +58,7 @@ static boolean nextLineIsAfterKaigyou = FALSE;
 
 /* Private Methods */
 static void drawLineFrame(Bcom_WindowInfo *info);
-static void copyMsgToStrVar(char *m);
+static void copyMsgToStrVar(const char *m);
 static void msgget_at_r();
 static void msgget_at_a();
 
@@ -108,7 +108,7 @@ void msg_setStringDecorationType(int type) {
 	msgDecorateType = type;
 }
 
-void msg_putMessage(char *m) {
+void msg_putMessage(const char *m) {
 	int         w;
 	MyRectangle adj;
 	
@@ -339,7 +339,7 @@ static void drawLineFrame(Bcom_WindowInfo *i) {
 	ags_updateArea(i->x -8, i->y -8, i->width +16, i->height +16);
 }
 
-static void copyMsgToStrVar(char *m) {
+static void copyMsgToStrVar(const char *m) {
 	if (v_strlen(msg.mg_curStrVarNo -1) == 0) {
 		v_strcpy(msg.mg_curStrVarNo -1, m);
 	} else {
diff --git a/src/message.h b/src/message.h
index 4cdac21..eb94362 100644
--- a/src/message.h
+++ b/src/message.h
@@ -32,7 +32,7 @@ extern void msg_init();
 extern void msg_setFontSize(int size);
 extern void msg_setStringDecorationColor(int col);
 extern void msg_setStringDecorationType(int type);
-extern void msg_putMessage(char *msg);
+extern void msg_putMessage(const char *msg);
 extern void msg_nextLine();
 extern void msg_nextPage(boolean clear);
 extern void msg_hitAnyKey();
diff --git a/src/nact.c b/src/nact.c
index 5decd71..7371bea 100644
--- a/src/nact.c
+++ b/src/nact.c
@@ -52,8 +52,8 @@ MG コマンド: 表示時の ZH に依存
 */
 
 /* defined in hankaku.c */
-extern BYTE *zen2han(BYTE *src);
-extern BYTE *han2zen(BYTE *src);
+extern BYTE *zen2han(const BYTE *src);
+extern BYTE *han2zen(const BYTE *src);
 /* defined by hankan2sjis.c */
 extern char *hankana2sjis(int index);
 /* defined by cmd_check.c */
@@ -124,8 +124,8 @@ char* sys_getConvString(char term) {
 }
 
 /* 選択肢・通常メッセージ振り分け */
-void sys_addMsg(char *str) {
-	char *msg = NULL;
+void sys_addMsg(const char *str) {
+	const char *msg = NULL;
 
 	switch(msg_msgHankakuMode) {
 	case 0:
@@ -153,7 +153,7 @@ void sys_addMsg(char *str) {
 	}
 	
 	if (msg && msg_msgHankakuMode < 2) {
-		free(msg);
+		free((char *)msg);
 	}
 }
 
diff --git a/src/nact.h b/src/nact.h
index 8d8442e..fc2ed1a 100644
--- a/src/nact.h
+++ b/src/nact.h
@@ -45,7 +45,7 @@ extern int *getCaliVariable();
 extern int *getVariable();
 extern char *sys_getString(char term);
 extern char *sys_getConvString(char term);
-extern void sys_addMsg(char *str);
+extern void sys_addMsg(const char *str);
 extern void sys_setHankakuMode(int mode);
 extern char *sys_getConstString();
 
@@ -110,7 +110,7 @@ typedef struct {
 	/* メッセージ関連 */
 	msg_t msg;
  	boolean   is_msg_out;          /* 通常メッセージを表示するか */
-	void (*msgout)(char *msg);     // 通常以外(DLL等)のメッセージ表示関数
+	void (*msgout)(const char *msg);     // 通常以外(DLL等)のメッセージ表示関数
 	
 	/* 選択肢関連 */
 	sel_t sel;
diff --git a/src/sdl_core.h b/src/sdl_core.h
index 6225437..4fc8688 100644
--- a/src/sdl_core.h
+++ b/src/sdl_core.h
@@ -53,7 +53,7 @@ extern void sdl_setPallet(Pallet256 *pal, int src, int cnt);
 extern void sdl_drawRectangle(int x, int y, int w, int h, int cl);
 extern void sdl_fillRectangle(int x, int y, int w, int h, unsigned long c);
 extern void sdl_drawLine(int x1, int y1, int x2, int y2, unsigned long col);
-extern int  sdl_drawString(int x, int y, char *msg, unsigned long col);
+extern int  sdl_drawString(int x, int y, const char *msg, unsigned long col);
 extern void sdl_copyArea(int sx,int sy, int w, int h, int dx, int dy);
 extern void sdl_drawTT(int x,int y,int w,int h,const char *bitmap,int ww, boolean antialiased);
 extern void sdl_copyAreaSP(int sx, int sy, int w, int h, int dx, int dy, int sp);
diff --git a/src/sdl_draw.c b/src/sdl_draw.c
index f6c002e..e69cdeb 100644
--- a/src/sdl_draw.c
+++ b/src/sdl_draw.c
@@ -412,7 +412,7 @@ static void sdl_drawAntiAlias_8bpp(int dstx, int dsty, agsurface_t *src, unsigne
 	SDL_UnlockSurface(sdl_dib);
 }
 
-int sdl_drawString(int x, int y, char *msg, unsigned long col) {
+int sdl_drawString(int x, int y, const char *msg, unsigned long col) {
 	int w;
 
 	sdl_pal_check();
diff --git a/src/xcore.h b/src/xcore.h
index 24b4242..9715b6e 100644
--- a/src/xcore.h
+++ b/src/xcore.h
@@ -57,7 +57,7 @@ extern void Xcore_setForeground(unsigned long col);
 extern void Xcore_drawRectangle(int x, int y, int w, int h, unsigned long col);
 extern void Xcore_fillRectangle(int x, int y, int w, int h, unsigned long col);
 extern void Xcore_drawLine(int x0, int y0, int x1, int y1, unsigned long col);
-extern int  Xcore_drawString(int x, int y, char *msg, unsigned long col);
+extern int  Xcore_drawString(int x, int y, const char *msg, unsigned long col);
 extern void Xcore_copyArea(int sx, int sy, int w, int h, int dx, int dy);
 // extern void Xcore_drawTT(int x, int y, int w, int h, const char *bitmap, int ww, boolean antialiased);
 extern int  Xcore_eCopyArea(int sx, int sy, int w, int h, int dx, int dy, int t,int opt, boolean flg, int spCol);
diff --git a/src/xcore_draw.c b/src/xcore_draw.c
index 5bae52a..70c8a5e 100644
--- a/src/xcore_draw.c
+++ b/src/xcore_draw.c
@@ -172,7 +172,7 @@ void Xcore_drawLine(int x1, int y1, int x2, int y2, unsigned long col) {
 	}
 } 
 
-int Xcore_drawString(int x, int y, char *msg, unsigned long col) {
+int Xcore_drawString(int x, int y, const char *msg, unsigned long col) {
 	int w;
 	
 	if (x11_font->self_drawable()) {