While an illumination optical system is irradiating the surface of a contaminated standard wafer with illumination light, this illumination light is scanned over the surface of the contaminated standard wafer, then detectors of a detection optical system each detect the light scattered from the surface of the contaminated standard wafer, next a predefined reference value in addition to detection results on the scattered light is used to calculate a compensation parameter “Comp” for detection sensitivity correction of photomultiplier tubes of the detectors, and the compensation parameter “Comp” is separated into a time-varying deterioration parameter “P”, an optical characteristics parameter “Opt”, and a sensor characteristics parameter “Lr”, and correspondingly managed. This makes is easy to calibrate the detection sensitivity.