Disclosed is a substrate treating apparatus for performing a cleaning treatment on substrates. The apparatus includes an indexer block with an indexer robot, a treating block including a front face cleaning unit and a back face cleaning unit as treating units, and a reversing path block including a plurality of shelves on which substrates are placed, and having a reversing function. The indexer robot includes a guide rail, a base, an articulated arm, and a hand. The guide rail is positioned so as not to overlap a mount position of a substrate in the reversing path block.