PURPOSE: To detect double feeding of paper sheet surely by forming the image of side edges of paper sheets on a one-dimensional image sensor, detecting a thickness of paper sheet by the formed side edge image and, when the thickness is over a specified level, judging the feeding to be double feeding.

CONSTITUTION: Sheets of paper 10 (10a and 10b) on a paper sheet stand provided facing a contact section of a pair of upper and lower frictional rollers are separated and fed one by one by the rotation of a pair of upper and lower frictional rollers. In the course of a transfer route for the sheets of paper 10, a light source 26, projection lens 28, and a CCD line sensor 30 as a one- dimensional image sensor are located on the side of the sheets of paper 10. Then, an image of the side edges of the sheets of paper 10 illuminated by the light source 26 is formed on the line sensor 30 through the projection lens 28, and the output from the sensor 30 is input into a double feeding identification means. In the double feeding identification means, a thickness of paper sheet is detected and, when it is over a specified level, feeding is judged to be double feeding to stop paper sheet feeding operation.