A fixing device includes a heating member, a pressing member, a coil, a magnetic core, a path switching member switching a magnetic path between a first path and a second path, and a magnetism adjustment member. The magnetism adjustment member allows a passage of a magnetic flux from the magnetic core towards the heating member within the magnetic field range when the magnetic field path is switched to the first path, and shields the magnetic flux without allowing the passage of the magnetic flux within the magnetic field range when the magnetic path is switched to the second path. Further, the magnetism adjustment member has a plurality of ring-shaped portions formed of a single wire material having an endless shape. Each of the ring-shaped portions extends in a longitudinal direction of the magnetic core according to a size of the sheet.