PURPOSE: To decrease the power consumption in a stand-by mode by using a single oscillator to control the time constant of an oscillating circuit and therefore changing the oscillation frequency.

CONSTITUTION: The oscillation frequency can be changed by varying the value of a feedback resistance covering from an output terminal 6 through an input terminal 5 of an inverter 1. For instance, an instruction is given to a control terminal P1 or the voltage is supplied to the terminal P1 by external terminal control. Thus a transistor TRT1 is turned on and the value of a feedback resistance is set at R. Otherwise the voltage is supplied to a control terminal P2 to turn on both TRT2 and T3 at a time, and the value of the feedback resistance is set at R+R1. While the voltage is supplied to a control terminal P3 to turn on both TRT4 and T5 at a time, and the value of the feedback resistance is set at R+R2. In such a way, the power consumption can be reduced in a stand-by mode. The same effect is obtained by changing the value of a capacitor C and then varying the oscillation frequency.