A substrate processing apparatus includes a transferring unit disposed in a connecting part of a washing processing cell and an indexer cell. The transferring unit includes an inverting support portion for supporting a substrate in a horizontal posture, a feed supporting portion disposed at an interval in a vertical direction from the inverting support portion for supporting the substrate in the horizontal posture, and an interposing and inverting mechanism for inverting the substrate to be supported by the inverting support portion and bringing the inverted substrate to be supported by the inverting support portion again. A part of the substrate to be supported by a feed supporting portion is disposed in an inversion region for the substrate to be inverted by the interposing and inverting mechanism.