To provide a transmission power control system that controls transmission power at a fast tracking speed so as to keep excellent channel quality even in high-speed fading or the like.

A variable attenuator 12 and a transmitter 13 amplify power of a transmission signal at a transmitter side 10 and wirelessly transmit the amplified signal via antennas 17, 21, and a receiver side 20 receives the signal. A receiver 23 detects the received level of the received signal, a coefficient controller 26 detects amplitude distortion and distortion change quantities and a channel quality detector 27 detects an error rate respectively, and they give the result to a reception decision device 28. The reception decision device totally decides the quality of the received signal on the basis of the error rate and the amplitude distortion and distortion change quantities, generates a signal for designating the transmission power on the basis of them and the reception level, and sends back the signal via a transmitter 29. A transmission power controller 16 controls an attenuator and controls the transmission power of the transmission signal on the basis of the transmission power designation signal received via a receiver 15.