PURPOSE: To provide the title device with stable characteristice against the leakage of electric wave even when there is a large gap between the inner frame of a door and the outer frame of the same and permit the outer frame to be fixed to the inner frame surely, by bending the outer periphery of the inner frame of the door into L-shape.

CONSTITUTION: A door 13 is attached to an oven 2 openably and the outer peripheral flange A of the inner frame 3 of the door is bent into L-shape in a space 11 between the inner frame 3 of the door and the outer frame 7 of the same. The inner frame 3 of the door is fixed to the outer frame 7 of the same surely by receiving the pawl C of the inner wall of the outer frame 7 with the end face of the L-shape section B while the outer frame 7 is reinforced against the external force of the door by the L-shape section D of the inner frame 3 of the door. A distance (a) between the structural body 5 and the inner frame 3 of the door, the size (b) of a choke groove and the depth (c) of the choke groove keep the optimum dimensions to attenuate electric wave leaked out of a heating chamber 1, therefore, the electric wave leakage characteristics of the title device may be stabilized and it is very beneficial in use.