ORIGINAL SIZE DETECTION DEVICE

PROBLEM TO BE SOLVED: To make working efficiency excellent and to enable sensitivity to be finely adjusted by the simple operation of an operator even in the case of such a high-density original that the number of black pictures is large or the density of a surface part is high like a newspaper by providing a device with a sensitivity adjustment means adjusting the sensitivity of a size detection member. SOLUTION: The sensitivity adjustment means 21 is fitted to a width sensor 11 through a substrate 24 and the surface of the sensitivity change-over switch 22 of the adjustment means 21 is set in an identical direction to the surface of the light receiving part 16 of the light reflection type sensor of the size detection member. When the adjustment means 21 is operated by the operator, a driver 23 is inserted in the groove part of the switch 22 and the switch 22 is turned according to the density of the hand of the operator so that the sensitivity is adjusted. By switching the turning direction of the switch 22, the quantity of irradiation light A can be adjusted. Thus, since proper reflected light corresponding to the density can be obtained, a malfunction is prevented from being executed by the light receiving part 16 and the sensitivity is excellently adjusted.