An image reading apparatus includes a light source with a first luminescent portion that outputs light with a first wavelength range and a second luminescent portion that outputs light with a second wavelength range, the wavelength ranges being different from each other; a light-receiving portion that receives light reflected from an original irradiated by the light source; a scanning portion that shifts a reading position of the original in a vertical scanning direction by changing a relative position between the original and the light-receiving portion; a switching portion that alternately turns on the first and second luminescent portions when the scanning portion shifts the reading position, wherein a vertical scanning resolution for a first data obtained when the first luminescent portion is turned on is independently set from a vertical scanning resolution for a second data obtained when the second luminescent portion is turned on.