There is provided a placement position determining part that calculates a rising gradient of an output value of the infrared sensor every after passage of a first predetermined time and performs a placement position determining operation of determining that a placement position of a cooking vessel is improper when the rising gradient is smaller than a first threshold value, and the placement position determining part performs the placement position determining operation after a lapse of a second predetermined time from the start of heating, thereby accurately determining that the cooking vessel is improperly placed on a top plate and preventing overheating of the cooking vessel.