Sheet feeder, automatic sheet feeder, image reader, and image forming apparatus

A sheet feeder comprising:

• a stacker configured to stack a sheet stack;
• a sheet feeding member configured to contact the sheet stack on the stacker to feed each sheet of the sheet stack;
• an aligner movable in a sheet width direction of the sheet stack and configured to align a position in the sheet width direction of the sheet stack on the stacker;
• a switcher configured to switch the aligner from a separation state to a contact state without waiting for a feeding start instruction after the sheet stack is stacked on the stacker,
• the sheet stack on the stacker and the sheet feeding member separating from each other in the separation state,
• the sheet stack on the stacker and the sheet feeding member contacting with each other in the contact state;
• a size specifying unit configured to specify a size in the sheet width direction of the sheet stack on the stacker;
• a position sensor configured to acquire the position of the aligner in the sheet width direction;
• and
• circuitry configured to delay a switching completion time from the separation state to the contact state when an error between a position of the aligner in the sheet width direction of the sheet stack corresponding to the size in the sheet width direction of the sheet stack specified by the size specifying unit and a position of the aligner in the sheet width direction of the sheet stack acquired by the position sensor is greater than a given error, to be later than the switching completion time when the error is equal to or smaller than the given error.