A paper feeder has a sheet stacking surface for stacking sheets, a paper feeding roller which is in contact with the uppermost surface of the sheets stacked on the sheet stacking surface to feed sheets, a movable separation slope surface against which the stacked sheets abut and which is rotatable between a first position and a second position that differ in the inclination angle made between it and the sheet stacking surface, and a separation control cam for rotating the movable separation slope surface between the first position and the second position. The angle made by the movable separation slope surface and the sheet stacking surface is set to be smaller than the angle when the sheets are separated so that the forward end portion of the pile of sheets stacked will not deform and when the sheets are fed by the paper feeding roller, the angle is set to be the angle when the movable separation slope surface separates the sheets by using the separation control cam.