A fixing unit of an image forming apparatus includes a coil arranged along an outer surface of the heating member and generating a magnetic field, a first core arranged opposite the heating member with respect to the coil and forming a magnetic path, a second core so fixed between the first core and the heating member with respect to a direction in which the coil generates the magnetic field, as to form the magnetic path together with the first core, a shielding member positioned outward of the second core and shielding the magnetism in the magnetic path, and a magnetism adjusting unit moving the shielding member outward of the second core to switch the position of the shielding member between a shielding position where the shielding member shields the pass of the magnetism and a retracted position where the shielding member permits the pass of the magnetism.