An apparatus includes a housing unit in which sheets are stacked, and a regulator in the housing unit including a body that has surfaces at which ends of the sheets are regulated. The apparatus further includes a stopper in the regulator, a retainer in the housing unit configured to engage with the stopper to lock the regulator to the housing unit, and a movement mechanism configured to move, when the body is pushed in a direction in which the regulator is to be moved, the stopper away from the retainer to disengage the stopper from the retainer.