The substrate treating apparatus includes a processing module and an index module on which a cassette having the substrate received therein is placed and that includes an index robot that transfers the substrate between the cassette and the processing module. The processing module includes a process chamber and a transfer chamber. The process chamber includes a support unit. The support unit includes a support on which the substrate is placed and a ring member that surrounds the substrate placed on the support and that is provided so as to be detachable from the support. The apparatus further includes a carrier storage unit that stores a carrier that is mounted on a hand of the main transfer robot or the index robot and on which the ring member is placed when the ring member is transferred by the main transfer robot or the index robot.