A method of polishing end point detection includes polishing a surface of a substrate; applying light to the surface of the substrate and receiving reflected light from the substrate during the polishing of the substrate; measuring reflection intensities of the reflected light at respective wavelengths; creating a spectral profile indicating a relationship between reflection intensity and wavelength from the reflection intensities measured; extracting at least one extremal point indicating extremum of the reflection intensities from the spectral profile; during polishing of the substrate, repeating the creating of the spectral profile and the extracting of the at least one extremal point to obtain plural spectral profiles and plural extremal points; and detecting the polishing end point based on an amount of relative change in the extremal point between the plural spectral profiles.