A fixing device includes a hollow, generally cylindrical open-sided stationary heat roll, a flexible fuser belt, a fuser pad, a rotatable pressure member, and a roll shape retainer. The heat roll is configured to heat an outer circumference thereof, and defines an elongated longitudinal side opening in one side thereof. The fuser belt is looped for rotation around the heat roll to transfer heat radially outward from the roll circumference. The fuser pad is held substantially stationary along the roll opening outward from the roll hollow and inward from the loop of the fuser belt. The pressure member is pressed against the fuser pad through the fuser belt to form a fixing nip. The roll shape retainer is disposed on the roll opening to retain the generally cylindrical shape of the heat roll.