A replacement belt unit for use with an image heating apparatus which includes an endless belt for heating an image on a recording material at a nip, a rotatable member for forming the nip between itself and the endless belt and for rotating the endless belt by rotation thereof, and a holding member for holding the endless belt from an inside of the endless belt, includes: a replacement endless belt; a cylindrical member for supporting the replacement endless belt at an inner surface of the replacement endless belt; and an engaging portion provided in a longitudinal end side of the cylindrical member and engageable with the holding member so that the cylindrical member is maintained in a fixed state relative to the holding member when the replacement endless belt is fitted around the holding member.