There is provided is a metal line structure in which no defect of blistering occurs on a surface of a Cu/Ni film or a Cu/Au/Ni film even if an Ni plating thickness is reduced. According to this metal line 1, in a Cu/Au/Ni film structure in which an Au film 13 and a Cu film 15 are successively laminated by electroless plating on an Ni film 12 formed by electroless plating, the Ni film 12 has a phosphorus content x of 10 wt %≦x≦15 wt %. It was discovered through experiments that the so-called high phosphorus content type Ni film 12 having a phosphorus content x of 10 to 15 percent by weight became a fine smooth film under a condition of a film thickness of 0.1 &mgr;m or greater.