A flat cable conductor has: a conductor made of copper or a copper alloy; a first plating film made of tin and/or a tin-copper alloy, the first plating film being formed around the conductor; and a second plating film made of an alloy of tin and a third element selected from Au, Ag, Ni, Ge, Zn and Bi, the second plating film being formed around the first plating film. The third element has a concentration of 0.01 or more and 80 or less wt % at an outer surface of the second plating film.