An image reading device including: concave first lens mirrors that are arranged in an array shape along a main scanning direction and that collimate scattered light reflected by an irradiated object and reflect the scattered light as a substantially parallel bundle of rays that are angled in a sub-scanning direction; planar mirrors that reflect light from the first lens mirrors; apertures that are arranged in an array shape and that allow light from the planar mirrors to pass through by way of openings that are arranged in an array shape and that are light-shielded therearound for selectively allowing light to pass through; concave second lens mirrors that are arranged in an array shape into which light from the apertures is incident and that reflect the light from the apertures as converged light; and light receivers that have light receiving areas on which light from the second lens mirrors is incident and that form images that correspond to light from the openings.