A microwave radiation antenna includes an antenna body having a microwave radiation surface; a processing gas inlet configured to introduce a processing gas into the antenna body; a gas diffusion space configured to diffuse the processing gas in the antenna body; a plurality of gas outlets provided in the antenna body and configured to discharge the processing gas into the chamber; a plurality of slots provided in the antenna body under a state where the slots are separated from the gas diffusion space and the gas outlets; and an annular dielectric member provided in the microwave radiation surface side of the antenna body to cover a slot formation region where the slots are formed. A metal surface wave is formed in the microwave radiation surface by the microwave radiated through the slots and the annular dielectric member and a surface wave plasma is generated by the metal surface wave.