The paper feeder comprises a first transport unit (5) to transport a sheet (S) on top of a paper stack (2) on a paper loading table (3), and a second transport unit (6) to discharge sheets transferred from the first transport unit toward a binding device. The first transport unit begins transporting the next sheet each time a sheet is discharged from the second transport unit. Image data for a specified printed portion on the first sheet in the paper stack is stored in memory (19) as reference data. A camera (14) is disposed above the paper stack and photographs a region corresponding to the specified printed portion on the topmost sheet. A control unit (18) compares the image data for the paper photographed by the camera with the reference data, and if the image data matches the reference data, the first transport unit operations are paused.