A substrate processing apparatus includes a substrate polishing unit 40 having a polishing pad for polishing a wafer W, and a top ring 41 for holding a wafer and pressing the wafer against the polishing pad. An elastic membrane 80 for holding a surface opposite to a polishing surface of the wafer W is attached to the top ring 41 as a consumable. The elastic membrane 80 is provided with a plurality of strain sensors 85 and 86 for measuring strain occurring in the elastic membrane 80 during polishing, and data of an amount of strain is read to a control device 15 by detection units 90 and 91. The control device 15 sets a processing condition such as a polishing recipe for the wafer W based on strain information of the elastic membrane 80 measured by the strain sensors.