Patent ID: 7995958

Claim:
An image forming apparatus comprising: an image forming section forming a toner image and transferring the toner image onto a sheet; and a fixing unit including a heating member and a pressure member, the fixing unit operable to fix the toner image onto the sheet while nipping and conveying the sheet between the heating member and the pressure member, wherein: the heating member has a sheet conveyed region that the sheet passes, the sheet conveyed region being set in accordance with the size of the sheet being conveyed, and the fixing unit further includes: a coil arranged along an outer surface of the heating member and generating a magnetic field, a fixed core arranged opposite to the heating member with respect to the coil and forming a magnetic path, a plurality of movable cores arranged between the fixed core and the heating member with respect to a direction in which the coil generates a magnetic field, to form the magnetic path together with the fixed core, and also arranged along the sheet conveyed region, a shielding member arranged along an outer surface of at least one movable core and shielding magnetism, and a magnetism adjustment unit rotating at least one movable core around a predetermined axis to switch the position of the shielding member between a shielding position where the shielding member is positioned inside the sheet conveyed region to shield the magnetism and a retracted position where the shielding member is positioned outside the sheet conveyed region to permit pass of the magnetism.