An image reading apparatus includes a light source which irradiates an original with light, an imaging unit which images by condensing reflected and scattered light from the original via a plurality of reflecting mirrors and imaging mirrors, and a photoelectric conversion unit which converts, into an electrical signal, the reflected and scattered light imaged by the imaging unit. The imaging unit is an imaging optical system which is adjusted such that the difference between the spectral characteristic at an end portion in the main-scanning direction of the image reading apparatus and that at the central portion in the main-scanning direction becomes 5% or less at the peak wavelength of the light source.