To sustain uniform generation of plasma constantly over a large area. In the surface wave excitation plasma processing device, a plasma source includes: a microwave generator, a microwave waveguide and a dielectric block; and a plasma source also includes: a microwave generator, a microwave waveguide and a dielectric block. The lid of a chamber is fixed onto the microwave waveguides in parallel, and the dielectric blocks disposed in the chamber. A reflecting plate is disposed between the dielectric blocks so that electromagnetic waves propagating through the dielectric blocks are prevented from advancing into the counterpart dielectric blocks as reflected waves. Consequently, the plasma sources are controlled independently. Furthermore, a side reflector is disposed at outer circumference of each of the dielectric blocks so that a standing waves of the electromagnetic waves propagating through the dielectric blocks is formed thus forming a large area standing wave mode of surface waves uniformly.