A fixing device includes: a fixing member that fixes a toner image on a recording medium; a pressure member that forms a fixing pressure portion between the pressure member and the fixing member by making pressure contact with an outer circumferential surface of the fixing member, the fixing pressure portion being passed through by the recording medium holding an unfixed toner image; a heat supplier that supplies heat to the fixing member; and a thermal diffusion member that diffuses heat on a surface of the fixing member by contact with the fixing member.