PURPOSE: To prevent an internal oscillation frequency from giving disturbance to a reception signal by providing a switching circuit to a basic oscillation circuit of a microcomputer and changing minutely the basic oscillation frequency.

CONSTITUTION: The basic frequency f1 of the microcomputer 5 is decided by a ceramic filter 6 and capacitors 7, 9. The frequency f1 is divided further internally and the waveform includes much harmonic components, they enter the antenna of a tuner part 1 directly or through peripheral circuits to give disturbance to the reception frequency. When the switch 12 is turned on, a switching transistor 8 turned on through a resistor 11 is turned off because its base potential reaches OV, the basic frequency f1 changes minutely into the frequency f2 because of the interposition of a capacitor 10. The minute change is a level not giving any effect to the signal processing of the microcomputer, but its harmonics are deviated to frequencies not giving distrubance to the reception frequency.