A fixing device comprising: an endless fixing belt that includes a resistance heating layer that generates Joule heat when electric power is fed thereto and a pair of electrode parts that feed electric power to the resistance heating layer; a pair of power feeding members that are each in abutment with an outer circumferential surface of a corresponding one of the electrode parts to feed electric power to the resistance heating layer through the electrode part; a fixing roller that is loosely inserted into the fixing belt; a pressure member that is in pressure-contact with an outer circumferential surface of the fixing belt to form a fixing nip; a pair of meandering prevention members that are each provided facing a corresponding one of sides of the fixing belt in a width direction of the fixing belt, and prevent the fixing belt from meandering in the width direction; characterized in that it further comprises: a pair of prevention member holders that each hold a corresponding one of the meandering prevention members, such that the meandering prevention member rotates independently from the fixing roller, wherein the meandering prevention members are each held so as to have a rotation center positioned inside a circle, where, when seen in a rotation axis direction of the fixing roller, the circle has a center coincident with a midpoint between two focal points of an ellipse approximating a belt rotation path of the fixing belt, and has a radius equal to a distance from the center of the circle to a straight line passing through a rotation center of the fixing roller and a center of the fixing nip in a rotational direction of the fixing roller. an endless fixing belt that includes a resistance heating layer that generates Joule heat when electric power is fed thereto and a pair of electrode parts that feed electric power to the resistance heating layer; a pair of power feeding members that are each in abutment with an outer circumferential surface of a corresponding one of the electrode parts to feed electric power to the resistance heating layer through the electrode part; a fixing roller that is loosely inserted into the fixing belt; a pressure member that is in pressure-contact with an outer circumferential surface of the fixing belt to form a fixing nip; a pair of meandering prevention members that are each provided facing a corresponding one of sides of the fixing belt in a width direction of the fixing belt, and prevent the fixing belt from meandering in the width direction; characterized in that it further comprises: a pair of prevention member holders that each hold a corresponding one of the meandering prevention members, such that the meandering prevention member rotates independently from the fixing roller, wherein the meandering prevention members are each held so as to have a rotation center positioned inside a circle, where, when seen in a rotation axis direction of the fixing roller, the circle has a center coincident with a midpoint between two focal points of an ellipse approximating a belt rotation path of the fixing belt, and has a radius equal to a distance from the center of the circle to a straight line passing through a rotation center of the fixing roller and a center of the fixing nip in a rotational direction of the fixing roller. a pair of prevention member holders that each hold a corresponding one of the meandering prevention members, such that the meandering prevention member rotates independently from the fixing roller, wherein the meandering prevention members are each held so as to have a rotation center positioned inside a circle, where, when seen in a rotation axis direction of the fixing roller, the circle has a center coincident with a midpoint between two focal points of an ellipse approximating a belt rotation path of the fixing belt, and has a radius equal to a distance from the center of the circle to a straight line passing through a rotation center of the fixing roller and a center of the fixing nip in a rotational direction of the fixing roller.