A photosensor includes a light emitting element that radiates light onto an object to be detected and a light receiving element that has a light-receiving surface for receiving light radiated from the light emitting element. An incident light regulation portion covering the light-receiving surface is provided on a path along which the light radiated from the light emitting element directed toward the light-receiving surface, and the incident light regulation portion transmits light having an incident angle less than a predetermined value and blocks light having the incident angle greater than or equal to the predetermined value among light incident on the light receiving element.