A spring wire with a hardness of 50 to 56 HRC is subjected to first and second shot peening processes within a warm working temperature range of 150 to 350° C. In the first shot peening process, a first shot of a shot size of at least 1.0 mm is used. In the second shot peening process, a second shot smaller in shot size than the first shot is sued. Through these shot peening processes, compressive residual stress is imparted to the spring wire. The spring wire includes a residual stress increase part, residual stress peak part, and residual stress decrease part. In the residual stress decrease part, a part including a compressive residual stress magnitude equivalent to the magnitude of the compressive residual stress at a surface of the spring wire exists at a region at a depth exceeding the permissible pit depth.