Induction heating unit and fixing device and image forming apparatus including this

An induction heating unit configured to inductively heat a heating member being rotated in a predetermined rotating direction by magnetic flux, comprising:

• a housing;
• a magnetic flux generating source fixed to the housing so as to extend in a sheet width direction intersecting the rotating direction and configured to generate the magnetic flux;
• a core member made of magnetic material, secured to the housing and configured so as to make a magnetic path through which the magnetic flux passes;
• and
• a securing member made of thermal contraction material and contracted by being heated at predetermined temperature to secure the core member to the housing,
• wherein the core member is an arch core extending in an arch shape along the rotating direction, the arch core including one end part arranged at an upstream side in the rotating direction, another end part arranged at a downstream side in the rotating direction and a protrusion part between the one end part and the other end part toward a direction intersecting the rotating direction,
• the housing includes a hole part into which the protrusion part is inserted,
• the securing member has an external diameter larger than an internal diameter of the hole part and is formed in a second ring shape fitted onto a distal end part of the protrusion part penetrating through the hole part.