A Ni plating is applied on a base metal in a metal strip form, and a brightener-free Sn-(1 to 4% by mass)Cu plating is applied on the Ni plating. The metal strip is heat-treated at a temperature at or above the melting point (solidus line) of a Sn-(1 to 4% by mass)Cu alloy to form a Cu-Sn compound layer or a Cu—Ni—Sn-compound layer on the Ni plating layer and a Sn layer or a Sn—Cu-ally layer on the Cu—Sn compound layer or the Cu—Ni—Sn-compound layer. The metal strip is further fabricated into a connector.