An image forming apparatus includes an image forming portion that forms a toner image on a recording material, and a first rotatable member and a second rotatable member, which form a nip therebetween in which the toner image, formed on the recording material by the image forming portion, is heated. A belt unit includes an endless belt that externally heats the first rotatable member, and a supporting mechanism rotatably supporting the endless belt. A moving mechanism moves the belt unit so as to be movable between a contact position and a spaced position. In addition, a controller executes a process in which one of the belt unit with a new endless belt and a new belt unit with a new endless belt is moved to the contact position, and then, the new endless belt is rotated for a predetermined time by the first rotatable member.