A fixing device includes a rotating body, an endless belt, a base material of the endless belt being made of a heat-resistant resin having a glass transition temperature of 140° C. or more, a heater configured to heat at least one of the rotating body and the endless belt, a sliding sheet contacting an inner circumferential surface of the endless belt, a base material of the sliding sheet being made of a heat-resistant resin having a glass transition temperature of 140° C. or more, a pressure pad, the endless belt and the sliding sheet being interposed between the pressure pad and the rotating body, and grease provided between the endless belt and the sliding sheet. The grease includes a base oil made of a fluorine oil and a thickener made of a solid lubricant containing fluorine. The consistency of the grease is 330 to 385 at 25° C.