The control section of sheet material detection apparatus makes the luminous light emitting with predetermined amount of photophore, to determine whether in one first reference sheet detection zone. When the first reference sheet is not or not region, sheet material sensing sensor moves up the spacing for making a reservation for movement. When the first reference sheet is in region, the distance between this detection sheet material sensing sensor is stored with the first reference sheet. Control unit executes the second reference sheet of same treatment. When two detection ranges are correct, then control section determines that an output from piece detection sensor is correct, and is the detection process of a certain amount of photoemissive document of luminous quantity today. When the distance that two are detected be it is incorrect, then output be determined as mistake and a certain amount of light from optical transmitting set increase a step-length.
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