An image sensor unit includes: a light source including a light emitting element on a light emitting surface; a light guide that causes light from the light source to be incident on a light incident surface facing to the light emitting surface, ejects the light from a light ejecting surface and illuminates a document; a rod lens array that images reflected light from the document; a sensor substrate on which a photoelectric conversion element is mounted, the photoelectric conversion element converting the reflected light imaged by the rod lens array into an electric signal; and a frame that supports the light source, the light guide, the rod lens array and the sensor substrate, wherein positioning sections are provided on an opposite side of the light emitting surface of the light source and at a part of the frame which is disposed at the opposite side of the light emitting surface.