PURPOSE: To prevent main vibration in oscillation actuation from being drawn into spurious vibration by controlling constituent elements so that the growth coefficient of the main vibration in the oscillation actuation will be greater than that of the spurious vibration.

CONSTITUTION: Between C-MOS inverter and the electric power source, current control circuit A is provided and when the electric power source is put to work, one pulse is supplied to input terminal (b) of circuit A. Thus, circuit A is so constituted that a voltage applied to inverter T will rise gradually. In consequence, the electric power voltage is low in electric power feed, i.e. oscillation actuation and mutual conductance gm is suppressed low, preventing spurious vibration. In the stationary oscillation state, circuit A conducts to apply the electric power voltage direct to inverter T. Thus, since mutual conductance gm is suppressed low, drawing into the spurious vibration can be prevented only by attaching the simple circuit.