A microwave emission mechanism includes: a transmission path through which a microwave is transmitted; and an antenna section that emits into a chamber the microwave transmitted through the transmission path. The antenna section includes an antenna having a slot through which the microwave is emitted, a dielectric member through which the microwave emitted from the antenna is transmitted and a closed circuit in which a surface current and a displacement current flow. A surface wave is formed in a surface of the dielectric member. The closed circuit has at least: an inner wall of the slot; and the surface and an inner portion of the dielectric member. When a wavelength of the microwave is λ0, a length of the closed circuit is nλ0±δ, where n is a positive integer and δ is a fine-tuning component including 0.