A microwave plasma processing apparatus which easily ensures uniformity and stability of plasma in response to changes of process conditions and the like. The microwave plasma processing apparatus generates plasma of a process gas in a chamber by microwave and performs plasma processing to a work to be processed by using the plasma. On a plate composed of a conductor covering the outer circumference of a microwave transmitting board, two or more holes for propagating microwave from an edge part of the microwave transmitting board to an inner part of the plate are formed. Volume adjusting mechanisms and adjust the volume of the holes to adjust impedance of each unit when the microwave transmitting board is divided into individual units to which each of the holes belongs, and electric field distribution of the microwave transmitting board is controlled.