PURPOSE: To prevent radio wave jack by a malicious 3rd party by sending a selective call signal and a different code at each transmission of the selective call signal from a base station to a terminal station and allowing the terminal station to make a call from the base station effective when both the selection signal and the code are correct.

CONSTITUTION: When a terminal station (x) is selected by a selection control section 10 in a base station (y), a call signal generating section 11 generates a call signal of the selected terminal station (x), a code generating section 12 generates a code different at each transmission of the call signal, a synthesis section 13 synthesizes the call signal and the code and a transmission section 14 sends a synthesized signal F0. On the other hand, when a reception section 15 of the selected terminal station (x) receives the signal F0, a call signal check section 16 detects the call signal in the signal F0 and sends the code in the signal F0 to a code coincidence check circuit 18 when the call signal is correct. Moreover, a code generating circuit 17 generates a code, the code coincidence check section 18 identifies the code with the code in the signal F0 and starts an amplifier 19 when the code is correct. In this case, the code generating section 17 generates the same code as the code of the code generating section 12 of the basic station (y) and different at each reception of the call signal asynchronously.