At a frame 26 in a microwave plasma processing apparatus 100, numerous horizontal spray gas nozzles 27 formed therein injection holes A and numerous vertical gas nozzles 28 formed therein injection holes B are fixed. A first gas supply means 50 injects argon gas through the injection holes A into an area near each dielectric parts 31a. A second gas supply means 55 injects silane gas and hydrogen gas through the injection holes B into a position at which the gases do not become over-dissociated. The gases injected as described above are raised to plasma with a microwave transmitted through each dielectric parts 31a. Since the vertical gas nozzles 28 are mounted at positions at which they do not block the flow of plasma traveling toward a substrate G, ions and electrons do not collide with the vertical gas nozzles 28 readily.