A spectral detector includes a light source, a sample cell in which a sample flows therein, an optical sensor, an optical system that guides light from the light source to the sample cell and guides light from the sample cell to the optical sensor, the optical system has a spectroscope for dispersing light and the spectroscope is arranged between the light source and the sample cell or between the sample cell and the optical sensor, and a housing integrally including a lamp house part for housing the light source and an optical system housing part for housing at least the sample cell and the optical system. Since the lamp house part and the optical system housing part are integrated to constitute the housing, heat is easily transmitted from the lamp house part to the optical system housing part, and the time until the entire detector reaches thermal equilibrium is shortened.