To generate surface wave excitation plasma efficiently. A surface wave excitation plasma generator (10) comprising an annular waveguide (2), and a dielectric tube (3). The annular waveguide (2) has an inlet (2a) for introducing a microwave M, an end plate (2b) for reflecting the microwave M being introduced and propagating through the waveguide, and a bottom plate (2c) on which slot antennas (2d)are formed at a predetermined interval. Assuming the wavelength of the microwave M in the waveguide is g, the length from position b through positions c, d, e to position f on the bottom plate (2c), i.e. the circumferential length pD1 of the annular waveguide (2), is set at 2g and the positions b, c, d, e, f are set at an interval of g/2. Since the slot antennas (2d) are arranged at two positionsc and e, the interval between these two slot antennas (2d) is equalized to the wavelength in the waveguide.