An image sensor includes a light source; a bar-shaped light-guiding element having a first light-emitting section, which propagates light from the light source and irradiates an document from an oblique direction, and a second light-emitting section emitting light in a carrying direction of the document; a lens converging the light reflected from the document; a sensor receiving the light passed through the lens; a reflector disposed on the opposite side of the light-guiding element, by reflecting the light from the second light-emitting section such that an optical path of the light emitted from the second light-emitting section is located between the lens and the document, and irradiating the document from an oblique direction; and first and second light-scattering layers formed in areas opposed to the first and the second light-emitting sections, respectively, in the light-guiding element.