A mobile station 200 includes a receiving field level detecting unit 213 to convert a level of a wireless signal into an RSSI output, and a wireless frame timing deciding unit 214 to decide a wireless frame timing from the transient characteristic of the RSSI output. By deciding the wireless frame timing from the RSSI output, synchronous establishment can be realized even when the mobile station 200 does not include a demodulation circuit. The mobile station can perform the synchronous establishment without being increased in size.