Patent ID: 7369801

Claim:
An image forming apparatus, comprising: an image carrier which holds a developer image in an electrostatic manner; and a fixing apparatus which melts and fixes the developer image onto a recording medium to which the developing material image has been transferred, the fixing apparatus comprising: a first roller member fixed at a predetermined position and rotated by a drive mechanism; a second roller member having a shaft member, the second roller member being press-fitted against the first roller member by a pressure applying mechanism via a bearing member connected to the shaft member; an elastic layer formed at least at one of the first roller member and the second roller member; a conductive layer formed outside of the elastic layer; an inductive heating device including a coil, the inductive heating device supplying inductive heating to the conductive layer by a magnetic field generated from the coil, thereby heating the conductive layer; and a hardness change detecting mechanism which senses movement of the pressure applying mechanism in a non-contact manner with the pressure applying mechanism to detect expansion of an outer periphery face of the first roller member or the second roller member due to thermal expansion caused by the inductive heating, the hardness change detecting mechanism including: a light emitting element; a light receiving element which receives light from the light emitting element; and a light shield member provided at the bearing member, and due to the movement of the pressure applying mechanism, the light from the light emitting element to the light receiving element is shielded by the light shield member, thereby detecting a hardness change of the first roller member or the second roller member.