An image reading device includes a light source; a light guiding member; an imaging optical system that reflects the light, which faces a first direction from the object, in a second direction intersecting the first direction by a reflective plane disposed in the first direction of the object, that makes the light, which is reflected by the reflective plane, converge toward the second direction by an emission portion disposed in the second direction of the reflective plane, and that images an erect equal-magnification image of the object in the second direction of the emission portion; and an optical sensor that is disposed in the second direction of the emission portion of the imaging optical system, and detects the erect equal-magnification image that is imaged by the imaging optical system, in which the light guiding member is disposed at an object side of the emission portion in the first direction.