Fixing device and image forming apparatus

A fixing device to fix a toner image onto a recording medium formed with the toner image, the fixing device comprising:

• a rotatable endless fixing belt being operable between a non-expanded state and a thermally expanded state;
• a pusher member disposed on an inner peripheral side of the fixing belt, the pusher member extending in a direction parallel with a rotation axis of the fixing belt;
• a pressure roller disposed on an outer peripheral side of the fixing belt, the pressure roller extending in the direction parallel with the rotation axis to form a fixing nip part by pressing the fixing belt against the pusher member;
• a heat source disposed on the inner peripheral side of the fixing belt, the heat source extending in the direction parallel with the rotation axis to heat the fixing belt;
• a power supply shutoff member disposed on the outer peripheral side of the fixing belt to shut off the supply of power to the heat source depending on a state of the fixing belt;
• and
• a heat radiation plate disposed on the outer peripheral side of the fixing belt to cover part of the fixing belt,
• wherein the heat radiation plate is disposed in a position which is spaced from the fixing belt in the non-expanded state and at which the heat radiation plate contacts the fixing belt when the fixing belt is in the thermally expanded state.