In a sheet feeder of the present invention, a groove-shaped concave provided on an inner surface of a bearing extends therethrough in a direction where a rotational shaft of a feed roller extends. A surface of the rotational shaft of the feed roller is supported on a pair of outer edges of the groove-shaped concave formed on the inner surface of the bearing. A bottom of the groove-shaped concave is substantially circular-arc and concentric with the inner surface of the bearing other than the groove-shaped concave. The bottom of the groove-shaped concave is formed at such a depth that the surface of the rotational shaft of the feed roller does not contact the bottom while the rotational shaft of the feed roller is supported on the outer edges of the groove-shaped concave.