FIXING UNIT AND IMAGE FORMING APPARATUS INCLUDING THE FIXING UNIT

A fixing unit and an image forming apparatus including the fixing unit. The fixing unit includes a heating roller having an internal space in which a heating source is disposed and a pressurizing roller facing the heating roller. The heating roller has a circular hollow pipe shape and includes a fixing nip forming part which forms a fixing nip between the fixing nip forming part and the pressurizing roller. The nip forming part can have a slim part disposed at a center thereof and a pair of deformation preventing parts formed at both ends of the slim part, each deformation preventing part having a thickness thicker than a thickness of the slim part.