The present invention is intended to realize a spectrometer which improves the wavelength resolution without being affected by the pitch of the photodiode array. The present invention is characterized by a spectrometer which comprises a wavelength dispersion device spectrally dividing the measured light beam and a photodiode array composed of a plurality of photodiodes that detect the spectrally divided light beams by the wavelength dispersion device and output photocurrents, and performs measurement using the outputs of the photodiode array; providing a deflecting means that deflects the measured light beams and changes the position where the measured light beams are detected by the above photodiode array, and measuring the characteristics of the measured light beam from the measured results for different deflection amounts.