PURPOSE: To prevent an idle operation by stopping a motor when a water flow detecting signal is not outputted from a flow switch within a defined operating time after starting said motor.

CONSTITUTION: When a flow switch FS is not turned on due to an idle operation even if a pressure switch PS is turned on, the whole input of a NAND gate N1 becomes H, the output keeps an L condition, and a timer T1 continues to count. When a defined time or more set by the timer T1 has elapsed, an output Q is turned to L and the input of an AND gate A1 becomes L, stopping the motor. Thereby, the breakage of a pump due to idle operation can be prevented.