Mobile station equipment for a mobile communication system includes a decision section for deciding accuracy of data of a first signal transmitted from a base station, and a first signal strength measuring section for measuring a signal strength of the first signal. The mobile station equipment further includes an inquiring section for transmitting a permission request signal for a stand-by state process to the base station according to at least one of the decided accuracy and a comparison result of the measured signal strength of the first signal and a first given threshold value. And, in the mobile station equipment, a stand-by control section waits for permissible information to be transmitted from the base station equipment based on the permission request signal, and starts a stand-by state process upon receiving the permissible information.