In a magnetron and a plasma waveguide through which a microwave oscillated from the magnetron moves, there is provided a plasma waveguide including a plurality of step parts formed at any one side on an inner side surface of the waveguide, and a block part of a predetermined height formed at any other side on the inner side surface of the waveguide, wherein the block part is formed at a side opposite to a boundary part between the plurality of step parts.
The present disclosure forms the step part having a height decreasing to a predetermined level formed within the waveguide, and provides the block part of the predetermined height at the inner side surface of the waveguide opposite to the step part of the waveguide. Thereby, a problem with microwave leaks involved in a 3-stub system penetrating through an overall waveguide and a problem with damage to an external system due to microwaves traveling outward may be effectively solved. Further, because the block part of the predetermined height provided at the inner side surface of the waveguide is located at an opposite surface to the step part, an effect of microwave concentration within the waveguide having a gradual reduction in height in a microwave propagation direction is maximized.