MONOCHROMATOR

A monochromator 100 includes: a diffraction grating 2 placed within a housing 1 so as to receive light from an entrance 11 and disperse the light into a spectrum from which a component of light having a set wavelength is to be extracted through an exit 12; an optical filter 92 to be removably inserted between the grating and the exit to remove light within a specific wavelength band which is out of the set wavelength; a rotary drive 5 for rotating the grating using a stepping motor; a wavelength-movement information setter 73 which sets wavelength-movement information to be used for rotating the grating from an original position to a rotational position corresponding to the set wavelength; and a wavelength-movement controller 71 which controls the rotary drive to initially rotate the grating to the original position and subsequently rotate it to the aforementioned rotational position based on the wavelength-movement information.