diff --git a/include/picrin/irep.h b/include/picrin/irep.h
index 2ef24cd7..f436dcbe 100644
--- a/include/picrin/irep.h
+++ b/include/picrin/irep.h
@@ -25,6 +25,7 @@ enum pic_opcode {
   OP_CSET,
   OP_JMP,
   OP_JMPIF,
+  OP_NOT,
   OP_CALL,
   OP_TAILCALL,
   OP_RET,
diff --git a/src/vm.c b/src/vm.c
index 0afeced4..6da02f41 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -390,8 +390,8 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value argv)
     &&L_OP_POP, &&L_OP_PUSHNIL, &&L_OP_PUSHTRUE, &&L_OP_PUSHFALSE,
     &&L_OP_PUSHINT, &&L_OP_PUSHCHAR, &&L_OP_PUSHCONST,
     &&L_OP_GREF, &&L_OP_GSET, &&L_OP_LREF, &&L_OP_LSET, &&L_OP_CREF, &&L_OP_CSET,
-    &&L_OP_JMP, &&L_OP_JMPIF, &&L_OP_CALL, &&L_OP_TAILCALL, &&L_OP_RET, &&L_OP_LAMBDA,
-    &&L_OP_CONS, &&L_OP_CAR, &&L_OP_CDR, &&L_OP_NILP,
+    &&L_OP_JMP, &&L_OP_JMPIF, &&L_OP_NOT, &&L_OP_CALL, &&L_OP_TAILCALL, &&L_OP_RET,
+    &&L_OP_LAMBDA, &&L_OP_CONS, &&L_OP_CAR, &&L_OP_CDR, &&L_OP_NILP,
     &&L_OP_ADD, &&L_OP_SUB, &&L_OP_MUL, &&L_OP_DIV, &&L_OP_MINUS,
     &&L_OP_EQ, &&L_OP_LT, &&L_OP_LE, &&L_OP_STOP
   };
@@ -534,6 +534,13 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value argv)
       }
       NEXT;
     }
+    CASE(OP_NOT) {
+      pic_value v;
+
+      v = pic_false_p(POP()) ? pic_true_value() : pic_false_value();
+      PUSH(v);
+      NEXT;
+    }
     CASE(OP_CALL) {
       pic_value x, v;
       pic_callinfo *ci;