Fixing device and image forming apparatus

A fixing device includes a heating belt, a heat source, a pressuring body, a pressing member and a sheet member. The heating belt is endless and heats a medium while being circulated. The heat source supplies heat to the heating belt. The pressuring body forms a nip with the heating belt, rotates so as to circulate the heating belt and presses the medium with the heating belt. The pressing member is disposed inside the heating belt and presses the heating belt against the pressuring body at the nip. The sheet member is held between the heating belt and the pressing member, attached to the pressing member at a center side portion and both end side portions in a longitudinal direction of the sheet member and has a heat shrinkable property. The both end side portions are shiftable in the longitudinal direction greater than the center side portion.