There is provided a substrate processing apparatus capable of stably holding a substrate and properly processing the substrate. The substrate processing apparatus is an apparatus that processes a substrate while rotating the substrate, with a place surface of the substrate being oriented in a horizontal direction. The substrate processing apparatus comprises a table including a rotatable base plate having a plurality of projecting members projected outward, and a rotation driving mechanism that rotates the base plate. The table can rotatably hold the substrate such that the projecting members contact the substrate from below with a gap formed between the substrate and the table. The substrate processing apparatus further comprises a pressure adjusting apparatus including a suction duct line having one end thereof being opened to the gap, and a suction mechanism connected to the other end of the suction duct line.