PURPOSE: To prevent the heating in the part not in contact with a toner support body, by changing the range of a resistance layer to be supplied with electricity according to the size of the toner support body.

CONSTITUTION: A toner support body is fed with the centerline in the longitudinal direction of a resistance layer 9 as a reference so as to be brought into contact with an offset preventive layer 10. The length of the layer 9 in this case is made roughly the same as the width of the toner support body having a large width, and the space between electrode layers 13, 14 is made roughly the same as the width of the toner support body having a small width so that electricity is fed only to the part between the layers 13 and 14 in the case of fixing the image with the toner support body having the small width and is supplied over the entire range of the layer 9 in the case of fixing the same with the toner support having the large width. Joule heat is generated only in the part of the layer 9 in the range supplied with electricity, by which the toner on the toner support body in contact with the layer 10 is melted and is fixed to the toner support body. The stripping of the offset preventive layer is thus prevented.