diff --git a/src/ags.c b/src/ags.c
index fc16a8f..1e8d5f0 100644
--- a/src/ags.c
+++ b/src/ags.c
@@ -120,7 +120,7 @@ boolean ags_check_param_xy(int *x, int *y) {
 	return TRUE;
 }
 
-void ags_init(const char *render_driver) {
+void ags_init(const char *render_driver, bool enable_zb) {
 	nact->ags.mouse_warp_enabled = true;
 	nact->ags.world_size.width  =  SYS35_DEFAULT_WIDTH;
 	nact->ags.world_size.height =  SYS35_DEFAULT_HEIGHT;
@@ -129,6 +129,9 @@ void ags_init(const char *render_driver) {
 	nact->ags.view_area.y = 0;
 	nact->ags.view_area.w = SYS35_DEFAULT_WIDTH;
 	nact->ags.view_area.h = SYS35_DEFAULT_HEIGHT;
+
+	nact->ags.enable_zb = enable_zb;
+	nact->ags.font_weight = enable_zb ? FONT_WEIGHT_BOLD : FONT_WEIGHT_NORMAL;
 	
 	sdl_Initialize(render_driver);
 	font_init();
diff --git a/src/ags.h b/src/ags.h
index 6efe960..28a34f4 100644
--- a/src/ags.h
+++ b/src/ags.h
@@ -113,7 +113,10 @@ struct _ags {
 	agsurface_t *dib;           /* main surface */
 	void (*eventcb)(agsevent_t *e); /* deliver event */
 
+	int font_weight;
+
 	bool mouse_warp_enabled;
+	bool enable_zb;
 	boolean noantialias; /* antialias を使用しない */
 	boolean noimagecursor; /* リソースファイルのカーソルを読みこまない */
 };
@@ -122,7 +125,7 @@ typedef struct _ags ags_t;
 
 
 /* 初期化関係 */
-void ags_init(const char *render_driver);
+void ags_init(const char *render_driver, bool enable_zb);
 void ags_remove(void);
 void ags_reset(void);
 
diff --git a/src/cmdz.c b/src/cmdz.c
index a9c43e5..ff1127d 100644
--- a/src/cmdz.c
+++ b/src/cmdz.c
@@ -115,8 +115,8 @@ void commandZB() {
 	/* メッセージ文字を太さを設定 */
 	int weight = getCaliValue();
 
-	nact->msg.MsgFontWeight = weight;
-	nact->sel.MsgFontWeight = weight;
+	if (nact->ags.enable_zb)
+		nact->ags.font_weight = weight;
 
 	DEBUG_COMMAND("ZB %d:", weight);
 }
diff --git a/src/font.h b/src/font.h
index 3ed2b4c..80e8c5d 100644
--- a/src/font.h
+++ b/src/font.h
@@ -32,6 +32,7 @@
 #define FONTTYPEMAX 2
 
 #define FONT_WEIGHT_NORMAL 4
+#define FONT_WEIGHT_BOLD 7
 
 extern void font_init(void);
 extern void font_set_name_and_index(int type, const char *name, int index);
diff --git a/src/message.c b/src/message.c
index 9df5cdf..e66c289 100644
--- a/src/message.c
+++ b/src/message.c
@@ -64,9 +64,8 @@ static void msgget_at_a();
 
 void msg_init() {
 	/* メッセージフォントの大きさ */
-	msg.MsgFontSize   = 16;
-	msg.MsgFontWeight = 7;
-	msg.MsgFont       = FONT_GOTHIC;
+	msg.MsgFontSize = 16;
+	msg.MsgFont     = FONT_GOTHIC;
 	
 	/* 各種色 */
 	msg.MsgFontColor             = 255;
@@ -141,7 +140,8 @@ void msg_putMessage(const char *m) {
 	// fprintf(stdout, "x=%d, y = %d, msg=%s\n", msgcur.x,msgcur.y,msg);
 	if (!msg.mg_dspMsg) return;
 	
-	ags_setFontWithWeight(msg.MsgFont, msg.MsgFontSize, msg.MsgFontWeight);
+	ags_setFontWithWeight(msg.MsgFont, msg.MsgFontSize, nact->ags.font_weight);
+
 	switch(msgDecorateType) {
 	case 0:
 	default:
diff --git a/src/message.h b/src/message.h
index 1028e75..489f909 100644
--- a/src/message.h
+++ b/src/message.h
@@ -44,7 +44,6 @@ extern void msg_mg6_command(int cmd);
 struct __message {
 	/* メッセージフォントの大きさ */
 	int MsgFontSize;
-	int MsgFontWeight;
 	int MsgFont;
 	
 	/* 各種色 */
diff --git a/src/selection.c b/src/selection.c
index 64ee1a8..cbe9547 100644
--- a/src/selection.c
+++ b/src/selection.c
@@ -93,7 +93,6 @@ void sel_init() {
 	
 	/* メッセージフォントの大きさ */
 	sel.MsgFontSize = 16;
-	sel.MsgFontWeight = 7;
 	
 	/* 各種色 */
 	sel.MsgFontColor             = 255;
@@ -302,7 +301,7 @@ static void init_selwindow() {
 		NOTICE("frameType is Default");
 		break;
 	}
-	ags_setFontWithWeight(FONT_GOTHIC, sel.MsgFontSize, sel.MsgFontWeight);
+	ags_setFontWithWeight(FONT_GOTHIC, sel.MsgFontSize, nact->ags.font_weight);
 	for (i = 0; i < regnum; i++) {
 		DEBUG_MESSAGE("%d:%s\n", i +1, elm[i]);
 		ags_drawString(r.x +2, r.y + i * (sel.MsgFontSize +2) +1, elm[i], sel.MsgFontColor);
diff --git a/src/selection.h b/src/selection.h
index 78abecb..d91786a 100644
--- a/src/selection.h
+++ b/src/selection.h
@@ -55,7 +55,6 @@ struct _selection {
 	
 	/* メッセージフォントの大きさ */
 	int MsgFontSize;
-	int MsgFontWeight;
 	
 	/* 各種色 */
 	int MsgFontColor;
diff --git a/src/xsystem35.c b/src/xsystem35.c
index 3e80081..129bab4 100644
--- a/src/xsystem35.c
+++ b/src/xsystem35.c
@@ -97,6 +97,7 @@ static char *fontname_tt[FONTTYPEMAX] = {DEFAULT_GOTHIC_TTF, DEFAULT_MINCHO_TTF}
 static char fontface[FONTTYPEMAX];
 
 static boolean font_noantialias;
+static bool enable_zb = false;
 static bool integer_scaling = false;
 /* fullscreen on from command line */
 static boolean fs_on;
@@ -210,7 +211,7 @@ static void sys35_init() {
 
 	v_init();
 	
-	ags_init(render_driver);
+	ags_init(render_driver, enable_zb);
 
 	for (i = 0; i < FONTTYPEMAX; i++)
 		font_set_name_and_index(i, fontname_tt[i], fontface[i]);
@@ -293,6 +294,8 @@ static void sys35_ParseOption(int *argc, char **argv) {
 			fs_on = TRUE;
 		} else if (0 == strcmp(argv[i], "-noantialias")) {
 			font_noantialias = TRUE;
+		} else if (0 == strcmp(argv[i], "-enable_zb")) {
+			enable_zb = TRUE;
 		} else if (0 == strcmp(argv[i], "-ttfont_gothic")) {
 			if (argv[i + 1] != NULL) {
 				fontname_tt[FONT_GOTHIC] = argv[i + 1];
@@ -354,6 +357,13 @@ static void check_profile() {
 			font_noantialias = TRUE;
 		}
 	}
+	/* Enable ZB command (font weight) */
+	param = get_profile("enable_zb");
+	if (param) {
+		if (0 == strcmp(param, "Yes")) {
+			enable_zb = TRUE;
+		}
+	}
 	/* Audio buffer size */
 	param = get_profile("audio_buffer_size");
 	if (param) {
diff --git a/xsys35rc.sample b/xsys35rc.sample
index 52501d7..24ffb6d 100644
--- a/xsys35rc.sample
+++ b/xsys35rc.sample
@@ -97,3 +97,10 @@
 #no_imagecursor: Yes
 
 # -----------------------------------------------------------
+
+# Enables the ZB command (change the font weight). It is disabled by default
+# because it makes the text too bold with our default fonts.
+# This option is experimental and may be removed in the future. See
+# https://github.com/kichikuou/xsystem35-sdl2/issues/44 for details.
+
+#enable_zb: Yes