It is an object of the present invention to provide a fixing apparatus with which the movement of heat to the fixing belt during warm-up is suppressed, and the time it takes for the heating roller temperature to rise can be shortened, by reducing the contact surface area between the fixing belt and the heating roller, and an image formation apparatus that makes use of this fixing apparatus, and a toner used therein. A separation member provided on the inside of the fixing belt forms a pair with a tension roller, and a switching device for switching the positions thereof switches the positions when a set temperature is detected by temperature sensing device installed on the heating roller, so that the contact surface area of the fixing belt on the heating roller is different during warm-up and during fixing.