A photosensor apparatus includes a light receiving element that receives reflection light of light which is illuminated onto a reference pattern image formed on a moving member, a first illuminating unit that enters regular reflection light to the light receiving element, a second illuminating unit that enters diffuse reflection light to the light receiving element, and a light receiving optical system that conducts the regular reflection light and the diffuse reflection light to the light receiving element. Preferably, the light receiving optical system includes a lens, constitutes an image forming optical system that forms the reference pattern image on a light receiving plane of the light receiving element with respect to the diffuse reflection light, and enters to the light receiving plane of the light receiving element only a part of regular reflection light, which is reflected from substantially the same region where the diffuse reflection light is received.