With the aspect shown in FIG. 5(c), a bypass heating wire 85b4 for linking inner edge portions of the two heating wires 8 constituting the bent portion 85b2 is provided. Accordingly, the current flowing through the bent portion is dispersed to the bypass heating wire 85b4, and it is possible to suppress locally high temperatures at the vertex portion of the bent portion 85b2. Note that there is no particular limitation on the number of bypass heating wires, and as shown in FIG. 5(d), it is also possible to provide two bypass heating wires 85b4 and 85b5, for example.
4-4. Aspect 4 of Bent Portion