A control device is provided with a switching valve mechanism and first and second actuators. The switching valve mechanism is provided with a valve element for switching which is located within a casing. The valve element can linearly move between an open position at which first and second pressure change chambers of the casing are communicated with each other and a closed position at which the communication is interrupted. The valve element is held at the open position and the closed position by a first holding mechanism (toggle spring). When a float ascends to a first water level, the first actuator moves the valve element from the closed position to the open position. When the degree of vacuum within a pressure detection chamber becomes a second degree of vacuum or less, the second actuator moves the valve element from the open position to the closed position.