Abstract: A microwave oven adapted to radiate microwaves of mutually reverse phases to minimize impedance variation of a waveguide in response to load change of foodstuff, thereby maintaining an output of the microwave at a constant level regardless of load amount of the foodstuff and maintaining an electric field distribution in a cavity at a constant level as well.

Abstract: A microwave oven is disclosed in which the structure of the wave guiding tube is improved such that the variation of the impedance is minimized in spite of the variation of the load of the food, thereby making it possible to maintain the output of the microwave oven at a constant level regardless of the load of the food. The microwaves are divided into a plurality of wave streams, and the wave streams are made to have different phases. The microwave oven includes an input wave guiding tube coupled with a magnetron, for receiving microwaves from the magnetron. A first output wave guiding tube communicates to the input wave guiding tube, for receiving the microwaves from the input wave guiding tube to diffusely irradiate the microwaves into a cavity. A second wave guiding tube communicates to the input wave guiding tube, for converting the microwaves to a phase different from that of the first wave guiding tube to irradiate them into the cavity.