A fixing device includes a fixing belt for fixing an unfixed toner image
onto a recording medium, a planar heating member for heating the fixing
belt, and a pressure roller. The heating member includes a ceramic heat
generating element having a PTC characteristic, and a
high-thermal-conductive heat diffusion member. The fixing belt is formed
in an endless shape and is supported around, at least, the
high-thermal-conductive heat diffusion member, thereby to be heated. The
ceramic heat generating element comes into contact with the fixing belt
over the full width thereof with the high-thermal-conductive heat
diffusion member interposed therebetween. The high-thermal-conductive
heat diffusion member comes into contact with the fixing belt over the
full width thereof and diffuses heat generated by the heat generating
element, in the traveling direction of the fixing belt.