| 摘要 |
PURPOSE:To detect the size of an original by forming an optical transmission path on the reverse surface of an original pressure plate so that one end faces contact glass and the other end part faces a photodetecting element directly or indirectly, and setting its direction in parallel to the optical path of irradiation light from a light source for original exposure. CONSTITUTION:The light source 21 moves forth and back once in the lighting state and the other end part of an optical fiber 51 faces the photodetecting element 53, so the light from the light source 21 does not reach the optical fiber 51 where the original D is present. When the light transmissivity of the original D is high, only light which is attenuated greatly reaches the optical fiber 51 and the light reaches the optical fiber 51 nearly without loss where the original D is not present to irradiate the photodetecting element through the optical fiber 51. For the purpose, the photodetecting element 53 which outputs a detection signal corresponding to the light which is not attenuated is known to decide which fixed forms size the original size corresponds to.
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