PURPOSE: To eliminate the replacement of filters by arranging them on individual image detectors adapted to simultaneously detect spectra scattered according to the wavelength, as shited perpendicular to the scattered surface.

CONSTITUTION: A light coming from a slit 21 is separated into spectra λl...λn with a grating and a prism. They irradiate image detectors 3, the output of which is processed with an amplifier 4, a scanner 5, an A/D converter 7, a memory 8 and the like to obtain data. The image detector 3 is composed of a plurality of detectors 31W33 and shifted perpendicular to the spectral surface (at the right angle to AA" in the drawing) and with both ends overlapping, cut filters 36W38 are inserted into the front of the photo detection surface of the detectors as required. This enables simultaneous measurement of multiple wavelength elminating complicated replacement of the filters thereby providing a spectrometer minimizing the mixing of stray light and light of higher order.