PURPOSE: To easily prevent the production of a beat frequency by varying a clock frequency of a microcomputer in the case of a communication channel in which a beat frequency might take place.

CONSTITUTION: When beat disturbance takes place in a reception frequency of, e.g. 8th channel, it is stored in a storage means 8a. When the 8th channel is read from the channel storage means during scanning, a high level signal is outputted from a control means 8 composed of a microcomputer, a transistor(TR) 9a of a frequency control circuit 9 is turned on and a capacitor 9b is connected in parallel with a capacitor 10b of a clock circuit 10. Since the capacitance of the capacitor is increased, the clock frequency to the control means 8 is lowered. Thus, the production of the beat frequency is easily prevented.