A fixing device for fixing an image on a recording material includes a cylindrical rotatable heater that is provided with a hole portion at least at a longitudinal end portion, and a driving member engaged with the longitudinal end portion of the heater to rotate the heater. The driving member is provided with a claw portion engaged with the hole portion of the heater. The image is fixed on the recording material by the heat from the heater. In addition, the heater is provided, at the other longitudinal end portion, with a slit extending toward a central portion, the slit being disposed at a position different from the hole portion with respect to a circumferential direction of the heater so as to overlap the hole portion in the longitudinal direction.