Patent ID: 7885591

Claim:
A fixing device comprising: a heating unit including an elastic portion and a heat source; and a pressurizing unit comprising a rotatable endless member that conveys a recording medium and a pressurizing member which presses the endless member against the elastic portion of the heating unit, an unfixed toner image being fixed to a recording medium by passing the recording medium, which carries an unfixed toner image, through a nip portion formed between the elastic portion of the heating unit and the endless member of the pressurizing unit, the pressurizing member of said pressurizing unit comprising an elastic member with a flat surface, and a biasing member that biases the elastic member toward a side of the elastic member that faces the recording medium, and, in use of the biasing member, biasing being performed such that an amount of deformation of the elastic member approaches a saturation region inside a region of said nip portion, the saturation region being defined by a maximum amount of deformation of the elastic member, wherein a nip region, which is constituted by not less than a pressure value at which the rate of change is not more than −30% compared with a deformation ratio in a load direction (%/(kgf/mm 2 ) of the elastic member of said pressurizing unit in a low pressure region (0 to 0.010 kgf/mm 2 ), accounts for not less than 50% of the entire nip region.