PURPOSE: To enable driving ability to be changed easily, by providing interrupting sections respectively in unit reverse amplifier circuits and connecting the unit reverse amplifier circuits in parallel in a combination as desired according to whether the associated interrupting sections is made conductive or not.

CONSTITUTION: Unit reverse amplifier circuits 11, 12,...1n constituting an oscillating circuit are provided respectively with interrupting sections 21, 22...2n. The unit reverse amplifier circuits are connected in parallel in a combination as desired according to whether the associated interrupting sections are made conductive or not. In manufacture of ICs, the interrupting sections to make conductive are selected so as to provide appropriate driving ability in accordance with scale of load exerted to the oscillating circuit and the selected interrupting sections are made conductive. Further, the interrupting sections 21, 22...2n are controlled electrically by control signals such that the driving ability is enhanced, when power is turned ON, to stabilize oscillation quickly and then the driving ability is decreased to smoothen the output waveform. If the driving ability is decreased unexpectedly, this decrease of ability is detected and the appropriate ability is recovered.