A controller monitors water temperature through the water temperature thermistor in a temperature sensor (48) when a water level sensor (43) is detecting the water level in a pot (41). When the water temperature exceeds 110 DEG , the controller makes a decision that the water level thermistor in the water level sensor (43) cannot perform normal detection and drives a pump to supply water. When water supply based on the temperature detected by the water temperature thermistor is carried out more than three times, a decision is made that scale has adhered to the water level sensor (43) and scale cleaning request is notified to the user. When the water level thermistor cannot perform normal detection, a decision is made whether adhesion of scale is the cause or not and scale cleaning request can be notified at an appropriate timing.