A substrate processing apparatus having a polishing unit for polishing a periphery of a substrate. The substrate processing apparatus includes: a polishing unit configured to polish a periphery of a substrate; an imaging module configured to take an image of the periphery of the substrate polished by the polishing unit; and an image processing section configured to inspect a polished state of the substrate based on the image taken by the imaging module. The imaging module is configured to take the image of the periphery of the substrate when the polishing unit is not polishing the periphery of the substrate.