a fusing device of an image forming apparatus and method thereof are provided . the fusing device and method comprise a conductive member having a linear portion for contacting a printing medium ; a fusing film for sliding on a circumference of the conductive member ; a pressing roller for contacting the fusing film in the linear portion , forming a fusing nip area , and rotating the fusing film ; and an induction heating unit for heating the conductive member by induction and generating heat , wherein the thickness of the conductive member in the fusing nip area is smaller than the thickness of the conductive member in other areas .