An attachably/detachably sheet feeding unit includes a main body part, a pair of side cursors, a pair of cursor racks, a pinion and a holding member. On the main body part having a bottom plate, a sheet is placed. The side cursors are supported by the bottom plate to slide in a width direction of the sheet to restrict a position of the sheet in the width direction. The cursor racks respectively extend from the side cursors in opposing directions in the width direction. The pinion is engaged with the cursor racks. The holding member has a shaft support part rotatably supporting the pinion, is attachable/detachable to/from the bottom plate, and then, is supported to the bottom plate to move in the width direction while the pinion is engaged with the cursor racks, and is fixed to the bottom plate in an optional position in the width direction.