A fixing device includes a heater including a first sealing portion and a second sealing portion disposed at a first lateral end and a second lateral end of a tube in a longitudinal direction of a fixing rotator, respectively. The first sealing portion includes a first inboard end distanced from a first lateral end of a heat generating portion with a first distance in the longitudinal direction of the fixing rotator. The second sealing portion includes a second inboard end distanced from a second lateral end of the heat generating portion with a second distance in the longitudinal direction of the fixing rotator. The second distance is smaller than the first distance. A driving force transmitter transmits a driving force to the fixing rotator or an opposed rotator and is disposed in a first lateral end side of the fixing device where the first sealing portion is disposed.