A sheet feeder includes a lift table, a first sheet-side restricting member, a second sheet-side restricting member, a suction conveyor, a rear-end restricting member, an upper distance-measuring sensor, a lower distance-measuring sensor, and processing circuitry. The first sheet-side restricting member and the second sheet-side restricting member restrict first ends and second ends opposite to the first ends, respectively, of sheets. The suction conveyor sucks and conveys a sheet floated. The rear-end restricting member restricts the sheets from moving in a longitudinal direction of the sheets. The upper distance-measuring sensor and the lower distance-measuring sensor measure a first distance and a second distance, respectively, to the first sheet-side restricting member or the second sheet-side restricting member. The processing circuitry compares measurement results of the first distance and the second distance to determine whether a distance between the first sheet-side restricting member and the second sheet-side restricting member is adequate.

A stacking apparatus according to an embodiment includes a stacking table, a first guide member, a second guide member, and a vibrator. The stacking table includes a stacking surface on which sheets are sequentially stacked. The first guide member is provided to stand on the stacking table. The first guide member restricts position of edges in a first width direction of the sheets stacked on the stacking table. The second guide member is provided to stand on the stacking table. The second guide member restricts position of edges in a second width direction of the sheets stacked on the stacking table. The second width direction intersects with the first width direction. The vibrator applies micro-vibration to at least one of the first guide member and the second guide member.