The following Patent Document 1 discloses an example of this type of conventional spectroscopic device. In this spectroscopic device, a plurality of dichroic mirrors which are different in rising wavelength of reflectivity are arranged in increasing or decreasing order of the wavelength to thereby construct a dichroic mirror array. A planar mirror is disposed at the light reflection side of the dichroic mirror array so as to oppose the dichroic mirror array. Furthermore, a light-receiving element array having a plurality of light-receiving elements arranged along the arrangement direction of the dichroic mirrors is disposed at the light transmission side of the dichroic mirror array.
When collimated light is obliquely made incident from the planar mirror side to a dichroic mirror located at one end in the thus constructed spectroscopic device, light having wavelengths longer than the rising wavelength of the reflectivity of the dichroic mirror is reflected from the diachronic mirror, and light having wavelengths shorter than the rising wavelength is transmitted through the diachronic mirror. The reflected light is reflected from the planar mirror and made incident to the adjacent dichroic mirror. Subsequently, the light reflection and transmission is repeated until the light reaches the dichroic mirror located at the other end. As described above, light beams having different wavelength ranges are, respectively, transmitted through the respective dichroic mirrors, so that the collimated light is spectroscopically separated. The light transmitted through each dichroic mirror is optically received by the light-receiving elements arranged along the arrangement direction of the dichroic mirrors.
Patent Document 1: Japanese Published Unexamined Patent Application No. H10-62246