To improve control performance in controlling the displacement of a piezo element while increasing or decreasing the amount of a current running through the piezo element functioning as an actuator, by repeating on/off-operations of a switching device for chopper control.

A voltage of the piezo element is measured synchronously with the completion of on/off-operations of a charging switch. Based on this, a control mode of the displacement of the piezo element is adjusted so that the voltage of the piezo element may be a targeted voltage.