Sheet feeder and image forming apparatus

The present invention is for separating upper and lower sheets. The sheet feeder includes a feed roller that conveys the sheet fed by a pickup roller in a sheet feeding direction and a retard roller rotated in a sheet feeding direction at a rotational velocity faster than that of the feed roller by interposing a torque limiter. Meanwhile, the retard roller is rotated at a velocity equal to that of the feed roller when a single sheet is nipped in the roller nip portion. The sheet feeder further includes a controller that performs control such that, when double sheet feeding occurs by the pickup roller, the sheet of the retard roller side projects ahead of the sheet of the feed roller side in the sheet feeding direction by virtue of the torque limiter, and then, the retard roller is rotated in a direction opposite to the sheet feeding direction.