PURPOSE: To form a homogeneous and dense Ni film having a uniform thickness and free from color shading and pinholes by allowing diethylenetriamine or the like to exist when Ni salt and a reducing agent for the salt are applied to a base material and the Ni salt is reduced.

CONSTITUTION: To an Ni plating soln. contg. Ni salt, a reducing agent for the salt and other suitable agents such as an alkalinity providing agent, a complexing agent and a pH buffer is added ≥1 kind among diethylenetriamine, ethylenediamine and imidazole as an additive. The resulting Ni plating soln. is coated or sprayed on a base material of glass, plastics, ceramics or the like, and an Ni film is formed by reduction. Said diethylenetriamine or the like may be applied separately when the Ni salt is reduced.