PURPOSE: To reduce weight and dimension by driving a piezoelectric actuator so that the compulsory displacement and vibration which are generated on the outer wall of a cylinder block by explosion are suppressed on the basis of the signals supplied from an engine revolution sensor and a vibration sensor.

CONSTITUTION: An engine revolution sensor 3 generates pulses according to the engine revolution, and a piezoelectric actuator 4 is fixed on the outer wall of a cylinder block, and a vibration sensor 5 is fixed on the outer wall of the cylinder block and detects the vibration of the cylinder block. A controller 6 outputs a feed/forward control signal on the basis of the detection signal supplied from the revolution sensor 3 and outputs a feedback signal on the basis of the detection signal supplied from the vibration sensor 5, and controls the actuator 4. Accordingly, the compulsory displacement generated immediately after explosion can be suppressed, and the vibration suppressing effect can be increased. The actuator is made lightweight and small-sized.