A plasma processing apparatus includes: a chamber having a processing space therein; a substrate support provided inside the processing space; an upper electrode provided above the substrate support with the processing space interposed therebetween; an emitter provided to emit electromagnetic waves into a plasma generation space and extending in a circumferential direction around a central axis of the chamber and the processing space; and a waveguide configured to supply the electromagnetic waves to the emitter; wherein the waveguide includes a resonator having a waveguide path therein, wherein the resonator includes a first short-circuiting portion constituting a first end of the waveguide path and a second short-circuiting portion constituting a second end of the waveguide path, wherein the second end of the waveguide path is electromagnetically coupled to the emitter, and wherein the second short-circuiting portion has a capacitance that short-circuits the waveguide path at a frequency of the electromagnetic waves.

A plasma processing apparatus includes: a processing container; a resonator configured to resonate electromagnetic waves to be supplied; a slot antenna connected to the resonator; and a transmission window configured to transmit the electromagnetic waves radiated from the slot antenna and supply the electromagnetic waves into the processing container, wherein the resonator includes: an input port including an inner shaft and an outer cylinder; an output port including an inner shaft and an outer cylinder; a power supply fin connecting the inner shaft of the input port and the inner shaft of the output port and provided in the resonator; and a ground fin connected to the outer cylinder of the input port and the outer cylinder of the output port at a same potential and provided to protrude within the resonator so as to be inserted between fins of the power supply fin.