PURPOSE: To detect distinguishingly ordinary paper sheets for copying and transparent resin sheets such as sheets for OHP from each other by providing two detecting means to detect the light diffusedly reflecting and the light specularly reflecting the light reflected from a sheet as a light source, and by logically processing these detected output value.

CONSTITUTION: In a sheet detecting device of a color electronic copying machine, light emitting elements 31 comprising LEDs are arranged facing the right direction and inclining at an angle of 45° in the left side in a device body 30, and a first and second light receiving elements 33 and 35 comprising photo diodes facing directly upward and inclining at an angle of 45° in the left direction at the center and in the right side in the body 30. Through holes 32, 34, and 36 are also formed along the orientation of the light emitting element 31 and each of the light receiving elements 33 and 35 in the device body 30. The light diffusedly reflected and the light specularly reflected after being reflected by a sheet 9 are detected by the first light receiving element 33 and the second light receiving element 35 respectively, and whether the sheet is ordinary paper sheet, OHP sheet, or non-sheet is judged according to the logical sum of the output of these lights.