Provided is a plasma processing apparatus capable of generating a uniform plasma by preventing a nonuniformity of a current flow in a slot antenna. A dielectric plate is disposed to close a top openinProvided is a plasma processing apparatus capable of generating a uniform plasma by preventing a nonuniformity of a current flow in a slot antenna. A dielectric plate is disposed to close a top opening of a plate cover and a slot antenna for generating plasma is disposed on the dielectric plate. By allowing an outer periphery of the slot antenna to make direct contact with an inner wall portion ofg of a plate cover and a slot antenna for generating plasma is disposed on the dielectric plate. By allowing an outer periphery of the slot antenna to make direct contact with an inner wall portion ofthe plate cover by using a conductive member having elasticity, when a microwave is supplied to slot antenna, to make an electrical resistance between the inner wall portion of the processing vessel the plate cover by using a conductive member having elasticity, when a microwave is supplied to slot antenna, to make an electrical resistance between the inner wall portion of the processing vesseland the outer periphery of the flat plate antenna substantially the same at any point in the entire circumference of the processing vessel is possible, so that magnitude of the microwave current flowiand the outer periphery of the flat plate antenna substantially the same at any point in the entire circumference of the processing vessel is possible, so that magnitude of the microwave current flowing in the slot antenna can be made approximately the same.ng in the slot antenna can be made approximately the same.