When an upper limit float switch Fu is closed after a lower limit float switch Fl is closed according to a rise of the level of water in a water tank 60, a solenoid water valve WV is closed and power supply to an electric motor for driving an auger 40 and a compressor connected to an evaporator 30 is then allowed. When the lower limit float switch Fl is opened, the solenoid water valve WV is opened and power supply to the electric motor and compressor is cut off. When the lower limit float switch Fl is opened, a time set longer by a predetermined time than the time for the water level in the water tank 60 to reach the upper limit from the lower limit is measured. When the lower limit float switch Fl is kept open due to suspension of water supply, the solenoid water valve WV is closed in response to the completion of measurement of the time. This can suppress power consumption of the solenoid water valve WV.