Plasma processing apparatus

A plasma processing apparatus which applies plasma processing to a substrate placed on a stage by turning process gas supplied into a process vessel into plasma, the apparatus comprising:

• a lift mechanism which, in the process vessel, moves down the stage to a standby position when the plasma processing is not performed and moves up the stage to a processing position when the plasma processing is performed;
• a holding member detachably holding a mask which is to cover an outer peripheral edge portion of the substrate, between the standby position and the processing position;
• and
• a positioning mechanism positioning the mask on the stage, wherein:
• the mask is held while being horizontally movable without being positioned by said holding member;
• and
• when the stage is moved up from the standby position toward the processing position, the mask is transferred from said holding member onto the stage, and the mask is positioned on the stage by said positioning mechanism.