A polishing apparatus can detect escape of a substrate from a top ring during polishing. The polishing apparatus including: a polishing table (10) having a polishing pad (11); a top ring (21); and a substrate escape detection section for detecting escape of the substrate from the top ring, including a light irradiation member (26) for irradiating an area of the upper surface of the polishing pad with light, a controller (32) for controlling the light irradiation of the light irradiation member, an image-taking member (27) for taking an image of the area irradiated with the light, and an information processing member (31) for processing information outputted from the image-taking member, wherein said controller controls the light irradiation member in such a manner that it performs light irradiation at least for a period of time during which the substrate is regarded as being in contact with the polishing pad.