An internal nonvolatile memory contains a program to be executed during a rewrite operation mode. During the rewrite operation mode a CPU core writes received rewrite data to an external nonvolatile memory according to a program in the internal nonvolatile memory. A first selector circuit transmits a first chip select signal to the external nonvolatile memory when a mode signal indicates a normal operation mode, and transmits the first chip select signal to the internal nonvolatile memory when the mode signal indicates the rewrite operation mode. Since the activation of the internal nonvolatile memory is inhibited during the normal operation mode, it is possible to prevent erroneous execution of the program in the internal nonvolatile memory during the normal operation mode, and to prevent data rewrite to the external nonvolatile memory.