Driving of a driving unit is controlled so as to satisfy relationship of L>|X+Y| (|X|≦X0, |Y|≦Y0), wherein a distance between an outside end of a separation claw in a width direction when a fixing unit and the separation claw are at respective reference positions and a side end of a sheet, which is winding around a heating roller, in the width direction is L, a displacing amount of the fixing unit detected by a first detecting unit is X, a maximum displacing amount of the fixing unit is X0, a displacing amount of the separation claw detected by a second detecting unit is Y, and a maximum displacing amount of the separation claw is Y0.