PURPOSE: To hold a noise damping effect by installing a mounting board as opposed to a high voltage transformer in terms of a microwave oven provided with a noise prevention device which prevents the generation of unbalanced noise where the noise prevention device is provided with a choke coil and a capacitor mounted on a circuit board fixed on an oven main body by way of the mounting board.

CONSTITUTION: A mounting board 36 which supports a noise prevention device 35 is laid out in such a fashion that the rear side 36a of the mounting board 36 may be opposed to a high voltage transformer 34. A common mode choke coil 35b and a capacitor 35c are installed to a circuit board 35a which fixes them with a bottom frame 35b by way of the mounting board 36. The mounting board 36 shuts off the magnetic flux from a high voltage transformer 34a, thereby reducing the magnetic flux which affects the common mode choke coil 35b of the noise prevention device 35 and the capacitor 35c. It is, therefore, possible to maintain a damping effect on noise.