PURPOSE: To change a transmission output without affecting the line quality of an adjacent carrier signal by controlling the transmission output at a control signal generation circuit to simultaneously monitor an AGC voltage and the error pulse signal of an adjacent channel.

CONSTITUTION: A control signal generation circuit 101 of a multi-carrier signal reception station II simultaneously monitors the AGC voltage of a variable gain amplifier for each channel and the error pulse signal through a demodulator 213. Based on this monitored result, the circuit 101 outputs a control signal and transmits it through a transmitter 215 and a transmission/reception sharing equipment 206 to a transmission station I, and the transmission output is controlled through a variable attenuator 202 or the like for each channel of the transmission station. Thus, the transmission output can be changed without affecting the line quality of the adjacent carrier signal.