A substrate processing apparatus includes: a processing container having a plurality of processing spaces formed therein; a substrate stage arranged in each of the plurality of processing spaces; a rotary arm including at least one end effector capable of holding a substrate and having a rotation axis located at a position equidistant from the plurality of processing spaces; a sensor provided on a back surface of the at least one end effector of the rotary arm, which is opposite to a substrate holding surface of the at least one end effector; and a rotation mechanism configured to rotate the rotary arm so that the sensor is moved to a position facing the substrate stage or the substrate placed on the substrate stage inside the processing container.