Abstract: An excitation beam from a laser is passed through a bandpass filter, and applied to a sample by a collimator lens. An optical adjusting part comprising a camera lens and a converging lens is provided for receiving scattered light from the sample, so that the camera lens receives the scattered light and converts the same to a parallel beam. The converging lens has chromatic aberration, and receives and converges the parallel beam from the camera lens. An inlet slit of a spectroscope is provided as an inlet port on a converging position by the converging lens. This inlet slit is a circular hole having a diameter of about 200 .mu.m. The inlet slit is arranged on a position for converging anti-Stokes-Raman scattered light through the chromatic aberration of the converging lens.