PURPOSE: To prevent the electrification of static electricity due to friction and to prevent dust and material scraps from sticking to a code plate by providing a code part and a character display part on a thin plate composed of a conductive base stock.

CONSTITUTION: Code pierce parts 16 and pierces 17 for code position detection are provided on the thin plate composed of the conductive base stock such as alminum or the like and the code plate 3 is constituted. Since the material of the code plate 3 is metal, electric charge is uniformly distributed, electricity is easily discharged, the electrification of the static electricity due to the friction is prevented, and thus, the sticking of surrounding dust and material scraps is reduced and read errors are prevented. Further, it is preferable to attach a transparent thin plate or a transparent sheet 25 provided with a size for covering the entire pierced part on the front side and back side of the thin plate to which piercing is performed. Since the entire pierce parts 16 and 17 are covered with the transparent thin plate 25 such as an acrilyc board or the like, the material scraps or the like are prevented from being hooked to the pierced parts and the stuck dust or the like can be easily removed by a brush for removing the dust.