A microwave oven includes a main casing with a cooking chamber, a door for opening and closing the cooking chamber, and a magnetron in the main casing, for heating food within the cooking chamber. The microwave oven further includes a power supply part, a first door switch closed while the door is closed to supply electric power from the power supply part into the magnetron, a monitor switch connected in series to the first door switch, being operated in reverse relative to the opening and closing of the first door switch, and a control part determining that the first door switch is in trouble where the first door switch and the monitor switch are not operated in reverse to each other, and preventing the electric power from being supplied into the magnetron when the door is opened while the first door switch and the monitor switch are both closed. With this configuration, the number of necessary switches are decreased and the circuits' structure is simplified, and thereby, the cost of production can be lowered and the stability of circuits can be improved.