To provide a plasma processing device that is capable of preventing dielectric window for introducing a micro wave from being damaged.

A plasma processing device 10 comprises: a processing chamber 11 in which a substrate S is accommodated; and a plasma generation unit 12 arranged adjacent to the processing chamber 11. The plasma generation unit 12 comprises: a waveguide 15 through which a micro wave propagates; a plasma generation chamber 16 connected to the waveguide 15; and a dielectric window 17 existing between the waveguide 15 and the plasma generation chamber 16 and introducing the micro wave propagating through the waveguide 15 into the inside of the plasma generation chamber 16. A plasma generation space G of the plasma generation chamber 16 includes a hemispherical curved space part sandwiched between a hemispherical curved surface and a hollow hemispherical inside curved surface concentrically arranged to oppose the hemispherical curved surface with a predetermined distance in-between and having a diameter larger than that of the hemispherical curved surface, and communicates with the inside of the processing chamber 11.