A fusing device for fusing a predetermined toner image on paper, and which controls the heating range of a fusing unit by inputting an eddy current generated by a transformer to a terminal corresponding to the size of paper selected from a plurality of terminals of the fusing unit. The fusing device includes a power supply unit to which a predetermined alternating current is input and which generates an induced current in response to the input alternating current, a fusing unit being resistance-heated and induction-heated by the induced current and fusing the toner image on the paper using the generated heat, and a controller for controlling the induced current supplied to the fusing unit according to the size of the paper.