An image forming apparatus, which receives a roll sheet and feeds the roll sheet to the image forming apparatus by conveyance means to record an image on the roll sheet, the image forming apparatus comprising: a pair of placement stages on which the roll sheet is to be placed; racks provided to the pair of placement stages, respectively; a pinion which is arranged between the racks, and operates in association with movement of the racks; a potentiometer which operates in association with rotation of the pinion; voltage detecting means for detecting a voltage value in accordance with a resistance value of the potentiometer; and calculation means for calculating a width of the roll sheet based on the resistance value of the potentiometer which varies in accordance with a distance between the pair of placement stages which move in association with each other by the racks and the pinion; characterized by a roller which is held in contact with flanges fixed to both ends of the roll sheet, and rotates in association with rotation of the flanges; roller driving means for driving the roller; rotatable members arranged on the pair of placement stages, respectively, the rotatable members rotating in association with the rotation of the flanges and retaining the flanges together with the roller; a lever which is arranged between the roller and the rotatable member of at least one of the pair of placement stages, and moves in accordance with presence and absence of the flanges; a shaft which rotates in association with the lever, and passes through the at least one of the pair of placement stages; a switch arranged at an end portion of the shaft; and roll sheet detecting means for detecting the presence and absence of the flanges in accordance with an output from the switch. a pair of placement stages on which the roll sheet is to be placed; racks provided to the pair of placement stages, respectively; a pinion which is arranged between the racks, and operates in association with movement of the racks; a potentiometer which operates in association with rotation of the pinion; voltage detecting means for detecting a voltage value in accordance with a resistance value of the potentiometer; and calculation means for calculating a width of the roll sheet based on the resistance value of the potentiometer which varies in accordance with a distance between the pair of placement stages which move in association with each other by the racks and the pinion; characterized by a roller which is held in contact with flanges fixed to both ends of the roll sheet, and rotates in association with rotation of the flanges; roller driving means for driving the roller; rotatable members arranged on the pair of placement stages, respectively, the rotatable members rotating in association with the rotation of the flanges and retaining the flanges together with the roller; a lever which is arranged between the roller and the rotatable member of at least one of the pair of placement stages, and moves in accordance with presence and absence of the flanges; a shaft which rotates in association with the lever, and passes through the at least one of the pair of placement stages; a switch arranged at an end portion of the shaft; and roll sheet detecting means for detecting the presence and absence of the flanges in accordance with an output from the switch.