PURPOSE: To keep transmission power stably and to reduce the connection time by operating a transmission power control loop only for a period of a prescribed time slot and feeding back a power control signal latched finally to a variable attenuation circuit.

CONSTITUTION: A difference between a level detection value inputted from an A/D converter circuit 61 and a reference value is calculated to generate an attenuation control signal to control a variable attenuation circuit l and the signal is inputted to a latch circuit 64. A timing signal generating circuit 65 applies a timing signal to the latch circuit 64 only for a transmission period of a time slot allocated to its own station. The latch circuit 64 latches the attenuation control signal fed from an arithmetic operation circuit 62 synchronously with the timing signal. Then a D/A converter circuit 66 converts the attenuation control signal from the latch circuit 64 into an analog signal and feeds it back to the variable attenuation circuit 1. Thus, the transmission power is stably kept and the feedback time constant is set to a smaller value, then the transmission power rises in a short time and the connection time is reduced.