A plasma processing apparatus (100) includes a plasma generation mechanism; a process container defining a process chamber configured to perform a plasma process on a target substrate; a substrate worktable configured to place the target substrate thereon inside the process container; and an exhaust mechanism configured to decrease pressure inside the process container. A wall (27a) of a support portion (27) for supporting a microwave transmission plate (28) is present in an area having an electron temperature of 1.5 eV or more during plasma generation. A covering portion (60) made of a heat resistant insulator, such as quartz, is disposed to cover the wall (27a).