Abstract: A processing apparatus includes a susceptor provided in a processing chamber and having an upper surface with a support area on which a semiconductor wafer is placed, and an aligning ring member movably arranged on the upper surface of the susceptor to surround the support area, the ring member defining the shift of the wafer placed on the support area and formed of a material having a thermal expansion coefficient smaller than that of the susceptor. A plurality of projections are provided on the peripheral portion of the upper surface of the susceptor at intervals along the ring member. A plurality of slots are provided in the aligning ring member for receiving the corresponding projections. The slots permit relative movement of the projection received therein in a radial direction of the ring member, but prohibit relative movement of the projections received therein in a rotating direction of the ring member as a whole.