A heater includes a plurality of heat-generating cells partitioned by a
boundary line arranged on a base body, and includes one resistive heating wire formed in each heat-generating
cell and having a zig-zag shape as a whole, the resistive heating wire formed by connecting a parallel wiring and a turn-back wiring formed so as to turn back the parallel wiring in a vicinity of the
boundary line between adjacent heat-generating cells. In the adjacent heat-generating cells, the resistive heating wire of a heat-generating
cell has an extension portion extending the parallel wiring past the
boundary line, and the resistive heating wire of the other heat-generating
cell is shortened or deformed so that a wiring of a portion facing the extension portion maintains an electrical insulation with the extension portion. The resistive heating wires of the adjacent heat-generating cells include extension portions alternately in a boundary line direction.