By flexographic printing or inkjet printing, insulating ink is applied on a wiring pattern in accordance with a predetermined printing pattern. The insulating ink is hardened, whereby an insulating layer is formed. A contact region of the wiring pattern that is used for electrical connection with a conductor other than the wiring pattern is not covered with the insulating layer. The printing pattern is delimited by the outline of a non-printing region including the contact region. The wiring pattern includes, in the non-printing region, a trunk wiring line leading, to the contact region, from a position on the wiring pattern at which the wiring pattern overlaps with the outline and a branch wiring line extending from a point on at least one side of the trunk wiring line and terminating without making contact with the outline.