an excitation wavelength sweeping type raman spectroscopic apparatus including a wavelength variable laser source , a laser beam converging unit for irradiating a laser beam from the laser source onto a specimen , a bandpass filter for selecting a beam of a predetermined wavelength out of raman scattered light beams emitted from the specimen , and a photodetecting unit for detecting the beam selected by the bandpass filter . in the apparatus , a raman spectrum of the specimen is measured by sweeping the wavelength of the laser beam .