According to one embodiment, a plasma processing apparatus includes a chamber, a plasma generator, a gas supplier supplying, a placement part, a depressurization part, and a supporting part. The supporting part includes a mounting part positioned below the placement part and provided with the placement part, and a beam extending from a side surface of the chamber toward a center axis of the chamber. One end of the beam is connected to a side surface of the mounting part. The beam includes a space connected to an outside space of the chamber. A following formula is satisfied, t1>t2, when a thickness of a side portion on the placement part side of side portions of the beam is taken as t1, a thickness of a side portion on an opposite side of the placement part side of the beam is taken as t2.