A sheet feeder, which is included in an image forming apparatus, includes a pair of first regulators and a pair of second regulators. The pair of first regulators is disposed movable in a width direction of a recording medium loaded on the sheet loader and is configured to contact a side end of the recording medium and regulate a position of the recording medium in the width direction. The pair of second regulators is configured to be detachably attachable to multiple attachment positions of the sheet tray selectably.