A fusing device and an image forming apparatus including the fusing device are provided, the fusing device having a structure that ensures a stable transport of a printing medium by preventing a printing medium from deviating from a transport path between a transfer nip and a fusing nip. The fusing device includes a heating member, a pressing member to contact the heating member to form a fusing nip, and a guide member to guide a printing medium to the fusing nip. An end of the guide member is shaped such that a height of the end decreases as the end extends from a center thereof to opposite sides thereof, and disposed closer to the heating member than to the pressing member, with respect to an imaginary line extending from the fusing nip.