A method of detecting an end point of polishing of a wafer, comprising the steps of: using a color identifying sensor for recognizing a color component of light by applying light from a light source and by converging reflected light to an optical fiber to cause the color identifying sensor to previously recognize a color component of a substance of a wafer which must be polished; displaying an ON-state when the color component is recognized and an OFF-state when the color component is not recognized; one point (except for the central point) of the surface of the rotating wafer is irradiated with light emitted from the color identifying sensor to cause the color identifying sensor to detect the number of times (m) of off-states; and determining an end of polishing of the wafer when the detected number of times (m) coincides with the number (n) of off-states indicating an optimum end point of polishing of the wafer.