PURPOSE: To facilitate assembly of a control circuit by only connecting the main circuit side with the electrode sides of a water receptacle and a suspended water tans, and thereby forming an automatic operation system both for water supply and exhaust.

CONSTITUTION: A pump control unit PU is provided with screw terminals EAWEE connected to a common electrode ec2 of a suspended water tank 2, an exhaust level electrode el2, a lower electrode eu2, an upper electrode ea2, and a full level electrode eh2. The unit PU is also equipped with No.1, No.2 sensing parts to sense individually whether the distance between terminals EA-EC and that between EA-ED are in continuity or not, and with a changeover part to perform changeover from water supply to exhaust and vice versa. When No.1 sensing part has sensed out of continuity in the condition that No.2 sensing part is sensing out of continuity in case, for ex., the water supply side is selected, it is judged that the in-service conditions are fulfilled as long as the No.2 sensing part does not sense continuity even through the No.1 sensing part senses continuity, thereafter and a pump motor IM is driven and controlled.