There is provided a plasma processing apparatus capable of performing a plasma process while surely supplying a gas. The plasma processing apparatus includes an outer gas supply member having gas supply openings for supplying a plasma processing gas and a jacket configured to support the outer gas supply member within a processing chamber and serving as a gas supply member supporting device. The jacket includes three supporting members installed so as to connect the outer gas supply member and a sidewall and arranged at a certain distance in a direction in which the outer gas supply member extends and mounts fixed to the sidewall so as to mount the supporting members therein. The supporting members include a first supporting member fixed to a first mount and a second supporting member movably supported in a second mount.