A plurality of microwave introduction windows are placed at the top wall of the reaction chamber. Microwaves of the same power are introduced into, e.g., two microwave introduction windows that are equivalent in location relationship with respect to the sidewall of the reaction chamber, while microwaves of different power are introduced into, e.g., two microwave introduction windows that are non-equivalent in location relationship with respect to the sidewall. Thus, a cost-effective plasma process apparatus is obtained which can realize uniform plasma processing even if the plasma being generated within the reaction chamber has varied load impedance.