A fixing device to fix a toner image on a sheet includes a flexible endless belt that rotates in a predetermined direction, an inner circumferential surface of which includes a fluorine-containing surface layer, a rotary member that contacts an outer circumferential surface of the belt, a fixed member fixed inside the belt to press against the rotary member via the belt, forming a nip portion therebetween, a lubricant applied between the belt and the fixed member, and a heat source to heat at least one of the belt and the rotary member. A surface of the fixed member that slidingly contacts the inner circumferential surface of the belt includes a fluorine-containing surface layer. One of the fluorine-containing surface layers is porous, and at least one of the fluorine-containing surface layers has a surface energy greater than a surface tension of the lubricant.