PURPOSE: To suppress the deterioration of a pump by providing a means to detect the abnormal driving of the pump caused by the nonexistence of water and stopping the driving of the pump when the abnormal driving is detected.

CONSTITUTION: A control circuit 11 to control the driving of a pump 7 according to an operation command from an operation display part 15 formed at the tip of a handle 13 and control the stopping of the driving of the pump 7 based on a signal from a piezoelectric buzzer 17 arranged closely to the pump 7 is provided. The piezoelectric buzzer 17 detects the oscillation of the pump 7 and outputs an electric signal corresponding to the oscillation. Further, after prescribed time passes, the pump 7 is temporarily stopped by inputting the signal from the piezoelectric buzzer 17 through an A/D input terminal, and the signal is compared with a previously set oscillation reference value. In the comparison, since an oscillation sound to occur when the pump 7 is driven becomes extremely high under a no load state, it is judged that water is run out when an integration signal level from the piezoelectric buzzer 17 exceeds the oscillation reference value.