A polishing state monitoring apparatus measures characteristic values of a surface, being polished, of a workpiece to determine the timing of a polishing end point. The polishing state monitoring apparatus includes a light-emitting unit for applying light from a light source to a surface of a workpiece being polished, a light-receiving unit for receiving reflected light from the surface of the workpiece, a spectroscope unit for dividing the reflected light received by the light-receiving unit into a plurality of light rays having respective wavelengths, and light-receiving elements for accumulating the detected light rays as electrical information. The polishing state monitoring apparatus further includes a spectral data generator for reading the electrical information accumulated by the light-receiving elements and generating spectral data of the reflected light, and a processor for calculating a predetermined characteristic value on the surface of the workpiece based on the spectral data generated by the spectral data generator.