An array of optical features is formed in a surface of a relatively thick growth substrate wafer. A block member serving as a scattered developer discharge prevention member is provided so as to block a path through which the developer scattered as a result of a conveyance operation of a supply screw serving as a developer conveying member moves toward a developer discharge port. The data buffer detects both whether the whole data buffer holds \u201c0\u201d data and whether the whole data buffer holds \u201c1\u201d data.