A pair of discretionary points on a principal surface of a block are coupled to each other with a metal wire having a length larger than a distance between the pair of discretionary points, liquid resin is applied to the principal surface so as to cover the metal wire and then cured, so that a resin-cured material is formed, and the upper-surface portion of the resin-cured material is removed together with an intermediate portion of the metal wire, and then the block is removed from the resin-cured material.