PURPOSE: To obtain a low-power consumption and stable oscillating circuit, by switching and connecting a one-stage inverter and three-stage inverters to the crystal oscillator in the crystal oscillating circuit at an oscillation start time and after stabilization of oscillation operation respectively.

CONSTITUTION: At an oscillation start time, the feedback circuit consisting of one- stage inverter IA is connected to crystal oscillator 10 as shown in the figure; and after stabilization of oscillation operation, the feedback circuit consisting of three- stage inverters IA, IB and IC is connected to crystal oscillator 10 as shown in the figure. For these connections, inverters are switched by a switch and so on. Consequently, oscillation transfers to stable oscillation rapidly without abnormal oscillation at an oscillation start time, and the oscillation operation can be continued with low power consumption after stabilization.