diff --git a/src/sys/nact.cpp b/src/sys/nact.cpp
index 70ea1e0..ee6fe56 100644
--- a/src/sys/nact.cpp
+++ b/src/sys/nact.cpp
@@ -163,7 +163,7 @@ void NACT::execute()
 	sco.skip_syseng_rev_marker();
 
 	// １コマンド実行
-	prev_addr = sco.addr();
+	sco.mark_cmd_start();
 	uint8 cmd = sco.getd();
 
 	if(set_palette && cmd != 'P') {
@@ -293,10 +293,8 @@ void NACT::execute()
 			if (is_message(cmd)) {
 				sco.ungetd();
 				message(0);
-			} else if (cmd >= 0x20 && cmd < 0x7f) {
-				sys_error("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			} else {
-				sys_error("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sco.unknown_command(cmd);
 			}
 			break;
 	}
diff --git a/src/sys/nact.h b/src/sys/nact.h
index d728561..a435de8 100644
--- a/src/sys/nact.h
+++ b/src/sys/nact.h
@@ -111,12 +111,8 @@ protected:
 	// コマンドパーサ
 	void execute();
 
-	// シナリオデータ
 	Scenario sco;
 
-	// アドレス、ページ管理
-	int prev_addr;
-
 	// 変数
 	uint16 var[512];
 	uint16 var_stack[30][20];
diff --git a/src/sys/nact_sys1.cpp b/src/sys/nact_sys1.cpp
index a47f5a2..b31e8e0 100644
--- a/src/sys/nact_sys1.cpp
+++ b/src/sys/nact_sys1.cpp
@@ -145,7 +145,7 @@ void NACT_Sys1::cmd_branch()
 	if(!condition) {
 		// 次の'}'命令までスキップする（ネストも考慮する）
 		for(;;) {
-			prev_addr = sco.addr();
+			sco.mark_cmd_start();
 			uint8 cmd = sco.getd();
 
 			if(cmd == '!') {
@@ -221,10 +221,8 @@ void NACT_Sys1::cmd_branch()
 			} else if (is_message(cmd)) {
 				sco.ungetd();
 				sco.skip(encoding->mblen(sco.ptr()));
-			} else if (cmd >= 0x20 && cmd < 0x7f) {
-				sys_error("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			} else {
-				sys_error("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sco.unknown_command(cmd);
 			}
 		}
 	}
@@ -547,20 +545,20 @@ void NACT_Sys1::cmd_a()
 
 void NACT_Sys1::cmd_b()
 {
-	// 未使用
-	sys_error("Unknown Command: 'B' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('B');
 }
 
 void NACT_Sys1::cmd_d()
 {
-	// 未使用
-	sys_error("Unknown Command: 'D' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('D');
 }
 
 void NACT_Sys1::cmd_e()
 {
-	// 未使用
-	sys_error("Unknown Command: 'E' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('E');
 }
 
 void NACT_Sys1::cmd_f()
@@ -597,26 +595,26 @@ void NACT_Sys1::cmd_g()
 
 void NACT_Sys1::cmd_h()
 {
-	// 未使用
-	sys_error("Unknown Command: 'H' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('H');
 }
 
 void NACT_Sys1::cmd_i()
 {
-	// 未使用
-	sys_error("Unknown Command: 'I' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('I');
 }
 
 void NACT_Sys1::cmd_j()
 {
-	// 未使用
-	sys_error("Unknown Command: 'J' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('J');
 }
 
 void NACT_Sys1::cmd_k()
 {
-	// 未使用
-	sys_error("Unknown Command: 'K' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('K');
 }
 
 void NACT_Sys1::cmd_l()
@@ -719,20 +717,20 @@ void NACT_Sys1::cmd_l()
 
 void NACT_Sys1::cmd_m()
 {
-	// 未使用
-	sys_error("Unknown Command: 'M' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('M');
 }
 
 void NACT_Sys1::cmd_n()
 {
-	// 未使用
-	sys_error("Unknown Command: 'N' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('N');
 }
 
 void NACT_Sys1::cmd_o()
 {
-	// 未使用
-	sys_error("Unknown Command: 'O' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('O');
 }
 
 void NACT_Sys1::cmd_p()
@@ -867,8 +865,8 @@ void NACT_Sys1::cmd_s()
 
 void NACT_Sys1::cmd_t()
 {
-	// 未使用
-	sys_error("Unknown Command: 'T' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('T');
 }
 
 void NACT_Sys1::cmd_u()
@@ -891,14 +889,14 @@ void NACT_Sys1::cmd_u()
 
 void NACT_Sys1::cmd_v()
 {
-	// 未使用
-	sys_error("Unknown Command: 'V' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('V');
 }
 
 void NACT_Sys1::cmd_w()
 {
-	// 未使用
-	sys_error("Unknown Command: 'W' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('W');
 }
 
 void NACT_Sys1::cmd_x()
diff --git a/src/sys/nact_sys2.cpp b/src/sys/nact_sys2.cpp
index 9d049f5..08e3c87 100644
--- a/src/sys/nact_sys2.cpp
+++ b/src/sys/nact_sys2.cpp
@@ -85,7 +85,7 @@ void NACT_Sys2::cmd_branch()
 	if(!condition) {
 		// 次の'}'命令までスキップする（ネストも考慮する）
 		for(;;) {
-			prev_addr = sco.addr();
+			sco.mark_cmd_start();
 			uint8 cmd = sco.getd();
 
 			if(cmd == '!') {
@@ -259,10 +259,8 @@ void NACT_Sys2::cmd_branch()
 			} else if (is_message(cmd)) {
 				sco.ungetd();
 				sco.skip(encoding->mblen(sco.ptr()));
-			} else if (cmd >= 0x20 && cmd < 0x7f) {
-				sys_error("Unknown Command: '%c' at page = %d, addr = %d", cmd, sco.page(), prev_addr);
 			} else {
-				sys_error("Unknown Command: %02x at page = %d, addr = %d", cmd, sco.page(), prev_addr);
+				sco.unknown_command(cmd);
 			}
 		}
 	}
diff --git a/src/sys/nact_sys3.cpp b/src/sys/nact_sys3.cpp
index bbe796c..82045ef 100644
--- a/src/sys/nact_sys3.cpp
+++ b/src/sys/nact_sys3.cpp
@@ -328,8 +328,8 @@ void NACT_Sys3::cmd_b()
 
 void NACT_Sys3::cmd_d()
 {
-	// 未使用
-	sys_error("Unknown Command: 'D' at page = %d, addr = %d", sco.page(), prev_addr);
+	// Unused
+	sco.unknown_command('D');
 }
 
 void NACT_Sys3::cmd_e()
diff --git a/src/sys/scenario.cpp b/src/sys/scenario.cpp
index 4a0dd0c..40f1dfd 100644
--- a/src/sys/scenario.cpp
+++ b/src/sys/scenario.cpp
@@ -14,7 +14,7 @@ void Scenario::skip_string(Encoding *enc, uint8_t terminator)
 
 void Scenario::get_syseng_string(char* buf, int size, Encoding *enc, uint8_t terminator)
 {
-	int start_addr = addr();
+	int start_addr = addr_;
 
 	int i = 0;
 	for (uint8_t c = getd(); c != terminator; c = getd()) {
@@ -22,7 +22,7 @@ void Scenario::get_syseng_string(char* buf, int size, Encoding *enc, uint8_t ter
 			ungetd();
 		int len = enc->mblen(ptr());
 		if (i + len >= size)
-			sys_error("String buffer overrun at %d:0x%x", page(), start_addr);
+			sys_error("String buffer overrun at %d:0x%x", page_, start_addr);
 		memcpy(&buf[i], ptr(), len);
 		i += len;
 		skip(len);
@@ -40,7 +40,7 @@ void Scenario::label_call(int label)
 		jump_to(label_stack.back());
 		label_stack.pop_back();
 	} else {
-		label_stack.push_back(addr());
+		label_stack.push_back(addr_);
 		jump_to(label);
 	}
 }
@@ -56,7 +56,15 @@ void Scenario::page_call(int target_page)
 		page_jump(pair.first, pair.second);
 		page_stack.pop_back();
 	} else {
-		page_stack.emplace_back(page(), addr());
+		page_stack.emplace_back(page_, addr_);
 		page_jump(target_page, 2);
 	}
 }
+
+[[noreturn]] void Scenario::unknown_command(uint8_t cmd) {
+	if (cmd >= 0x20 && cmd < 0x7f) {
+		sys_error("Unknown Command: '%c' at %d:0x%d", cmd, page_, cmd_start_addr);
+	} else {
+		sys_error("Unknown Command: %02x at %d:0x%d", cmd, page_, cmd_start_addr);
+	}
+}
\ No newline at end of file
diff --git a/src/sys/scenario.h b/src/sys/scenario.h
index fa3db57..00e1339 100644
--- a/src/sys/scenario.h
+++ b/src/sys/scenario.h
@@ -54,11 +54,15 @@ public:
 	void page_stack_pop() { page_stack.pop_back(); }
 	void page_stack_clear() { page_stack.clear(); }
 
+	void mark_cmd_start() { cmd_start_addr = addr_; }
+	[[noreturn]] void unknown_command(uint8_t cmd);
+
 private:
 	Dri adisk;
 	std::vector<uint8_t> data_;
 	int page_;
 	int addr_;
+	int cmd_start_addr;
 	std::vector<int> label_stack;
 	std::vector<std::pair<int, int>> page_stack;
 };