To equally feed processing gas (material gas) into a chamber.

A showerhead 10A for introducing material gas into the chamber 1 is provided in a surface wave exiting plasma processing device 100. The showerhead 10A is equipped with a first chamber 11 and a second chamber 12 which constitute a two-staged structure composed of an upper and a lower hollow chamber. The material gas is introduced into the first chamber 11 through a gas inlet port 14, transferred to the second chamber 12 passing through a two or more gas jet holes 11b bored in a distributing plate 11a, and discharged into the chamber 1 passing through two or more gas jet holes 12b bored in the a distributing plate 12a. At this point, a gas pressure gradient is small in the first chamber 11, and a gas pressure gradient gets smaller in the second chamber 12, so that the material gas is equally fed toward the processed substrate S. As a result, plasma processing is improved in uniformity.