PURPOSE: To generate a proper ALC voltage in response to the type of a radio wave by controlling a switching circuit with an output signal frequency-divided by a programmable counter so as to switch a charge/discharge circuit in a time constant circuit.

CONSTITUTION: A programmable counter 18 frequency-divides a signal from a pulse generator 20 by programming a frequency dividing ratio in response to the selective operation by a digital mode selecting means 11 so as to control a switching means Q1 of the charge/discharge circuit 21 so as to make the time constant proportional to the sum of pulse widths per unit time. The ALC voltage transmitted from an ALC voltage generating circuit 9 to a base of a transistor Q2 for amplification controls an ALC line connected to a variable gain amplifier 5 according to the time constant of a terminal 21b for time constant.