Grease composition for heat fixing devices and heat fixing apparatus

A heat fixing device comprising:

• a heating rotor;
• a slide portion on which the heating rotor slides during rotation;
• a pressure rotor disposed opposite the heating rotor, and
• a grease composition between the slide portion and the heating rotor, the grease composition containing a base oil and polytetrafluoroethylene,
• wherein the base oil contains a perfluoropolyether having at least one structure selected from the group consisting of a structure represented by formula (I) and a structure represented by formula (II) in the molecule, and
• wherein the base oil has a kinematic viscosity v40 of 800 mm2/s to 2500 mm2/s at 40° C. and whose kinematic viscosity v200 at 200° C. is 1/50 or less of the kinematic viscosity v40: