PURPOSE: To prevent deterioration of an ignition electrode, to prevent perforation by discharging and to eliminate a reinforcing plate by intermittently operating an ignition transformer for discharging the electrode in frequency exceeding an audible band.

CONSTITUTION: An ignition transformer control output from a microcomputer 1 is sent to an ignition transformer 2, a discharge occurs between an ignition electrode 3 and a ground 4 to be ignited. Here, the transformer 2 is a quiet transformer to be discharged in frequency exceeding an audible band. The transformer 3 is intermittently operated by an ignition transformer controller provided in the microcomputer 1, and discharging between the electrode 3 and the ground 4 is intermittently conducted. The control output of the ignition transformer is turned ON, for example, for about 2msec, and then turned OFF for about 2msec, and such an output signal is repeated, for example, for 30sec. Thus, deterioration of the electrode is prevented, and a reinforcing plate is eliminated.