PURPOSE: To suppress a rush current at the time of an excitation start by invariably starting the excitation of a load in the same phase of the AC voltage.

CONSTITUTION: The excitation of a transistor 25 is controlled by the voltage VB half-wave-rectified with the AC voltage VA, and the voltage VC thus obtained is applied to a microcomputer 18. When the voltage VB is a preset value, a high-frequency circuit relay 11 is driven to close a normally-opened contact 11a with no counting by a delay timer 18a, and the excitation to a high-frequency oscillating circuit 8 is started. When the voltage VB is the preset value or below, a preset time is counted by the delay timer 18a, the high-frequency oscillating circuit relay 11 is driven when the counting is completed, and the excitation to the high-frequency oscillating circuit 8 is started.