A control circuit (131) returns the drive frequency to a prescribed drive frequency and then conducts another drive frequency variation when the reduction rate of the power source voltage is greater than the reference reduction rate; i.e., when either a piezoelectric actuator A is driven at a drive frequency with low driving efficiency and high power consumption, or the actuator cannot be started up for any reason. Therefore, the time needed to detect startup failure is not extended, startup failures and the like can be immediately determined based on the reduction rate of the power source voltage, and less time is needed to make this determination. Accordingly, the process beginning with detecting abnormalities and ending with optimizing the drive signal can be conducted rapidly, and the power consumption can be reduced to conserve energy.