To prevent radiated noise from an oscillation circuit from entering an FM broadcast by adopting an oscillator whose nominal frequency multiplied by any natural number is not within an FM broadcast frequency band for an oscillator of a microcomputer.

In the case that an oscillator with a nominal frequency of 16MHz used in general is adopted for an oscillator 2C, noise signals with frequencies equivalent to a multiple of a natural number of 16MHz are produced from an oscillation circuit 2. A multiple of 5 of 16MHz corresponds to 80MHz. This frequency 80MHz has some FM broadcast programs in a frequency band of 76-90MHz of FM broadcast, and in the case of listening to an FM broadcast program in a room using the air-conditioner, noise from the oscillation circuit 2 is superimposed on the FM broadcast waves and a listener has difficulty in listening to the radio receiver. However, in the case of using the oscillator 2C with a nominal frequency of, e.g. 15.1MHz, a multiple of 5 of the frequency is 75.5MHz and a multiple of 6 of the frequency is 90.6MHz, then no noise peak is in existence in the frequency band of the FM broadcast. Thus, difficulty in listening to FM broadcast due to radiation noise from the oscillation circuit is avoided.