A fixing device includes a heat pipe, a fuser belt, a heater, a fuser pad, a pressure member, and a coupling mechanism. The heat pipe is formed of a sheet of metal bent into a generally cylindrical configuration with a pair of opposed longitudinal edges thereof spaced apart from each other to define a longitudinal slot therebetween. The fuser belt is looped for rotation around the heat pipe. The heater is disposed within the heat pipe to heat the heat pipe to conduct heat to the fuser belt. The fuser pad is accommodated in the longitudinal slot of the heat pipe inside the loop of the fuser belt. The pressure member is disposed parallel to the heat pipe with the fuser belt interposed between the fuser pad and the pressure member. The coupling mechanism includes a pair of first coupling portion and a pair of second coupling portions.