A preliminary-cured material permits reduced surface roughness of a roughening-treated surface, and increase of an adhesive strength between a cured object and a metal layer. The preliminary-cured material is obtained by advancing curing of an epoxy resin material that contains an epoxy resin, a curing agent, and a silica. The preliminary-cured material includes a first principal surface to be roughening-treated, and a second principal surface. The silica includes a first small particle-diameter silica whose particle diameter is not smaller than 0.01 μm but smaller than 0.5 μm, and a second large particle-diameter silica whose particle diameter is not smaller than 0.5 μm but not larger than 20 μm. The first small particle-diameter silica is localized to exist in large quantity on a side of the first principal surface, and the second large particle-diameter silica is localized to exist in large quantity on a side of the second principal surface.