Abstract: In a radio paging system, first and second radio units perform radio communication via a relay station. This system includes a radio selective paging receiver for receiving a radio wave from the relay station and generating a ringing tone to call a callee at the second radio unit when the first radio unit calls the second radio unit.

Abstract: To keep a constant gate bias voltage to prevent a saturation output power from being decreased even when a GaAs FET for power amplification is operated near the saturation region, current amplification of an output from an operational amplifier (23) is performed by a transistor (24), and a gate bias voltage (Vg) is supplied to the gate of a GaAs FET (1). The gate bias voltage (Vg) is fed back to one input terminal of the operational amplifier (23), and a voltage obtained through voltage-dividing resistors (21, 22) is supplied to the other input terminal so that the operational amplifier serves as a voltage follower.