A Cu—Sn layer and an Sn-based surface layer are formed in this order on the surface of a Cu-based substrate through an Ni-based base layer, and the Cu—Sn layer is composed of a Cu3Sn layer arranged on the Ni-based base layer and a Cu6Sn5 layer arranged on the Cu3Sn layer; the Cu—Sn layer obtained by bonding the Cu3Sn layer and the Cu6Sn5 layer is provided with recessed and projected portions on the surface which is in contact with the Sn-based surface layer; thicknesses of the recessed portions are set to 0.05 μm to 1.5 μm, the area coverage of the Cu3Sn layer with respect to the Ni-based base layer is 60% or higher, the ratio of the thicknesses of the projected portions to the thicknesses of the recessed portions in the Cu—Sn layer is 1.2 to 5, and the average thickness of the Cu3Sn layer is 0.01 μm to 0.5 μm.