An image forming apparatus including an image reading unit disposed in an upper portion of the image forming apparatus, an image forming unit disposed below the image reading unit to form an image on a sheet fed from a sheet roll, a pair of flange members attached to both lateral ends of the sheet roll in a width direction of the sheet roll, a sheet roll supporter disposed below the image reading unit in a rear portion of the image forming apparatus to support the sheet roll, an opening through which the sheet roll is set to the sheet roll supporter, and a guide assembly provided at upper and lower parts of the opening to position at least one of the pair of flange members attached to the sheet roll in the width direction to guide the sheet roll to the sheet roll supporter.