A first electrode pattern 25a and a second electrode pattern 25b, each composed of an opaque conductive fine line and a blank part 17 partitioned by the conductive fine line, have line segments 16a of the conductive fine lines 16, that face each other across a substrate 12, and the conductive fine line 16 in one of the first electrode pattern 25a and the second electrode pattern 25b is formed narrower in line width than that in the other of the first electrode pattern 25a and the second electrode pattern 25b only at the facing line segment 16a, thereby designed to have a non-uniform width.