Disclosed is an AC/DC type microwave oven. The AC/DC type microwave oven comprises a rotatable inverter which inverts a DC power source to an AC power source by means of a rotational force, a high voltage transformer which receives a common power source or an AC power inverted by the rotatable inverter and outputs a higher voltage and a magnetron which is driven by the high voltage outputted from the high voltage transformer and radiates a microwave, and further comprises a control unit which controls the operation of the rotatable inverter so as to output a stable frequency. The rotatable inverter comprises a motor, a commutator driven by the motor and a plurality of brushes, which are respectively contacted with an outer surface of the commutator. Therefore, the manufacturing cost is lowered, the attrition rate of the current is lowered, the energy lost by heat is decreased, the size of the microwave oven can be smaller, and the output frequency from the rotatable inverter can be controlled to be kept constant and the microwaves are also more stably radiated.