The heat and pressure rolls of a fusing apparatus for an electrophotographic copying machine are shifted into pressure contact with one another while a support sheet bearing a toner powder image passes therebetween, and are separated while the sheet is not therebetween. A driving mechanism drives both rolls when not in contact, while one of the rolls drives the other while in pressure contact. A shifting mechanism is actuated by a sheet detector for shifting the rolls into and out of contact.In another embodiment, the rolls are in light rolling contact, with no sheet passing therebetween, under the weight of one of the rolls idly mounted in place. A pressing mechanism presses the rolls into pressure contact, upon actuation by a sheet detector, while the sheet passes between the rolls.