A spectral distribution measuring device, comprising: an illumination unit configured to illuminate white light to a surface of an object being measured; a slit array having a plurality of slits formed in alignment at equal intervals; a linear image sensor including a light receiving face having a plurality of rectangular pixels adjacently arranged in alignment and a plurality of spectral light irradiated areas divided in each predetermined number of neighboring pixels; a plurality of areas being measured which is set on the surface of the object being measured, and reflects the light irradiated by the illumination unit to the plurality of slits; and a diffraction unit (17, 173) configured to diffract and disperse reflection light which is reflected from the areas being measured and has passed through each slit, the diffraction unit being disposed such that a direction where a diffraction image expands is rotated at an angle about the z-axis to a direction where the light receiving face expands, the z-axis being parallel to the light incident direction to the diffraction unit (17,173), so that an irradiated area corresponding to a measuring wavelength range of each predetermined order diffraction light, except for zero order diffraction light, of the diffraction image of each dispersed reflection light on the light receiving face is irradiated to the corresponding each spectral light-irradiated area, characterized in that: the spectral light-irradiated area includes a measurement area comprising one or more pixels that are used in spectral measurement and a non-measurement area comprising one or more pixels that are not used in spectral measurement. an illumination unit configured to illuminate white light to a surface of an object being measured; a slit array having a plurality of slits formed in alignment at equal intervals; a linear image sensor including a light receiving face having a plurality of rectangular pixels adjacently arranged in alignment and a plurality of spectral light irradiated areas divided in each predetermined number of neighboring pixels; a plurality of areas being measured which is set on the surface of the object being measured, and reflects the light irradiated by the illumination unit to the plurality of slits; and a diffraction unit (17, 173) configured to diffract and disperse reflection light which is reflected from the areas being measured and has passed through each slit, the diffraction unit being disposed such that a direction where a diffraction image expands is rotated at an angle about the z-axis to a direction where the light receiving face expands, the z-axis being parallel to the light incident direction to the diffraction unit (17,173), so that an irradiated area corresponding to a measuring wavelength range of each predetermined order diffraction light, except for zero order diffraction light, of the diffraction image of each dispersed reflection light on the light receiving face is irradiated to the corresponding each spectral light-irradiated area, characterized in that: the spectral light-irradiated area includes a measurement area comprising one or more pixels that are used in spectral measurement and a non-measurement area comprising one or more pixels that are not used in spectral measurement. the spectral light-irradiated area includes a measurement area comprising one or more pixels that are used in spectral measurement and a non-measurement area comprising one or more pixels that are not used in spectral measurement.