To rapidly perform changeover into fixed gain, without having to adjust each time, when automatic gain control is stopped.

A reception signal is branched by a distributor 6, in order to fixedly keep the output level of receiver concerning the change of a reception input level, and the branched signal is detected by a wave detector 7. Detected wave detection voltage is compared with a control voltage in the case of a desired output level and inputted to a counter 12. A counter output is subjected to upcount, when the wave detection voltage is higher than the control voltage and to downcount, when it is lower. The counted value is converted into an analog voltage by a D/A converter 13, so as to generate a differential voltage with the control voltage, and the differential voltage is added to the control voltage by an addition amplifier 14, to obtain a gain control voltage. Then the generated gain control voltage is inputted to the side of the fixed gain control of a changeover unit 9 for changing-over automatic gain control and fixed gain control. When changeover is made for fixed gain, the fixed gain control side of the changeover unit 9 is selected by a changeover signal by manual operation, and then the changeover signal is made to stops counting.