Laser sources output laser lights L1 and L2 having different wavelengths so as to increase an accuracy of an endpoint detection of polishing processing by enabling an accurate detection of a film thickness of a layer insulating film on a surface of a wafer to be polished by the CMP processing, the lights are emitted from a detection window via a beam splitter to the layer insulating film formed on the surface of the wafer to be polished by a pad, different optical detectors detect interference lights corresponding to the laser lights L1 and L2 reflected and generated from a surface of the layer insulating film and a pattern under the surface via the detection window, the beam splitter, and a dichroic mirror, the detection results are supplied to a film thickness evaluation unit 7, a film thickness of the layer insulation film is detected on the basis of a relationship between intensities of the reflected interference lights to the laser lights L1 and L2 or the intensity ratio, and an endpoint of polishing processing is determined when the film thickness is equal to a predetermined value.