Sheet feeder

A sheet feeder comprising:

• a lift table on which sheets are stacked, the lift table being movable in a vertical direction;
• a first sheet-side restricting member configured to restrict first ends of the sheets stacked on the lift table in a width direction of the sheets;
• a second sheet-side restricting member configured to restrict second ends of the sheets opposite to the first ends of the sheets in the width direction of the sheets;
• a suction conveyor configured to suck and convey a sheet floated from the lift table after the lift table is lifted;
• a rear-end restricting member at a center portion of the sheets in the width direction of the sheets, the rear-end restricting member configured to restrict the sheets stacked on the lift table from moving in a longitudinal direction of the sheets;
• an upper distance-measuring sensor at an upper portion of the rear-end restricting member, the upper distance-measuring sensor configured to measure a first distance to the first sheet-side restricting member or the second sheet-side restricting member;
• a lower distance-measuring sensor at a lower portion of the rear-end restricting member, the lower distance-measuring sensor configured to measure a second distance to the first sheet-side restricting member or the second sheet-side restricting member;
• and
• processing circuitry configured to compare a measurement result of the first distance with a measurement result of the second distance to determine whether a distance between the first sheet-side restricting member and the second sheet-side restricting member is within a threshold.