Document feeder, document reader, and image forming apparatus with improved accuracy of document skew correction

A document reader including a document feeder and reading document sheets fed by the document feeder one at a time, the document feeder feeding document sheets one at a time from a stack on a tray by pressing one or more pick-up rollers against an uppermost document sheet and guiding one edge of the document sheet, the one edge being one of two edges in a width direction, the document feeder comprising:

• a document size obtainer that obtains size information indicating a width of the document sheet;
• and
• a center-of-contact shifting mechanism that shifts a center of contact of each pick-up roller along an axial direction of the pick-up roller according to the obtained size information, the center of contact being a central point of an area where the pick-up roller is in contact with the document sheet, wherein
• each pick-up roller is in a barrel shape, and
• the center-of-contact shifting mechanism shifts the center of contact of each pick-up roller by axially tilting the pick-up roller relative to a surface of the document sheet.

An image forming apparatus comprising:

• a document feeder that feeds document sheets one at a time from a stack on a tray by pressing one or more pick-up rollers against an uppermost document sheet and guides one edge of the document sheet, the one edge being one of two edges in a width direction perpendicular to a document transport direction;
• and
• a document reader that reads document sheets fed by the document feeder one at a time, wherein
• the document feeder includes:
• a document size obtainer that obtains size information indicating a width of the document sheet;
• and
• a center-of-contact shifting mechanism that shifts a center of contact of each pick-up roller along an axial direction of the pick-up roller according to the obtained size information, the center of contact being a central point of an area where the pick-up roller is in contact with the document sheet, wherein
• each pick-up roller is in a barrel shape, and
• the center-of-contact shifting mechanism shifts the center of contact of each pick-up roller by axially tilting the pick-up roller relative to a surface of the document sheet.