To restrain a reflection loss of a beam emitted from an optical fiber, in a spectroscope using a PDA detector for detecting light intensity using a diffraction grating.

A refractive index matching means for matching a refractive index, for example, a parallel plane member or a spherical member is provided in an end part for emitting the beam in the fiber, in this spectroscope provided with the photodiode array(PDA) detector comprising a large number of photoreceiving elements for detecting the light intensity of each spectral component of the beam by separating the beam emitted from the fiber into its spectral components using the diffraction grating.