A spectroscope includes an optical fiber 218, a collimator optical system 231 for collimating signal light come out from the optical fiber 218, a spectroscopic element 233 for dispersing the signal light collimated by the collimator optical system 231, a detector 237 composed of a plurality of detector elements 237a disposed at least in a direction of dispersion and detecting the light dispersed by the spectroscopic element 233, and a focusing optical system 236 for focusing the signal light come out from the detector 237 onto a detecting surface of the detector 237. It is set such that the focusing optical system 236 makes a diameter of a spot of the signal light focused on the detecting surface of the detector 237 smaller than an arranged pitch of the detector 237 and a numerical aperture of the collimator optical system 231 is larger than that of the optical fiber 218.