To provide a composite plating technology by which a plated film having higher strength can be obtained without using a heat treatment method or a heating method.

As a plating liquid, a liquid comprising water, nickel sulfate, nickel chloride, boric acid, a brightener, a surfactant, carbon nanofibers and SiC fine particles is used. Desired mechanical properties can be obtained by adding hard fine particles. The addition amount of carbon nanofibers can be drastically reduced by adding hard fine particles. It is possible to maintain the smoothness of the plated film because the addition amount of the carbon nanofibers is small.