A fixing device includes a fixing member that is rotatable and heated by a heater; an endless belt member that is rotatable while being in contact with the fixing member; and a pressing member that is disposed inside of the belt member. The pressing member presses the fixing member with the belt member therebetween so as to form a fixing nip between the fixing member and the belt member, the fixing nip allowing a recording medium to pass therethrough to fix a toner image onto the recording medium. In an output region of the fixing nip from which the recording medium is output from the fixing nip, a curvature of a cross-sectional shape of an end portion of the belt member in a width direction is larger than a curvature of a cross-sectional shape of a middle portion of the belt member in the width direction.