Light emitted from a light-emitting element is reflected by a beam splitter and made incident upon an optical fiber, while light launched from the optical fiber passes through the beam splitter and is made incident upon a light-receiving element. A lens is provided to focus the light emitted from the light-emitting element to an end face of the optical fiber and also the light launched, as diffused, from the optical fiber. Further, an optical plate is provided to form a reflecting surface on the upstream side of the end face of the optical fiber.