Provided is a fixing device including a fixing member that fixes a toner image onto a recording material, a pressurizing member that forms a pressurizing portion, in cooperation with the fixing member, through which the recording material holding a non-fixed toner image passes, a heating member that includes a heat generating portion having a predetermined pattern shape and being energized to generate heat, and heats the fixing member, a supporting member that supports the heating member along an inner circumferential surface of the fixing member, and a thermal diffusion member that faces the supporting member with interposing the heating member, and diffuses heat from the heating member and conducts the heat to the fixing member.