reference to figures. [0140] First, as shown in FIG. 1(a), an electrical conductive material such as a noble metal, for example gold or palladium, and carbon is subjected to the screen printing method, a sputtering evaporating method or the like, thereby to form the conductive layer 2 on the whole surface of the support 1. [0141] Next, as shown in FIG. 1(b), two slits 3 a and 3 b parallel to the s