In mass%, C: 0.38 to 0.44%, Si: 2.00 to 2.30%, Mn: 0.79 to 1.25%, Cr: 0.10 to 0.43%, Ni: 0.15 to 0.35%, Cu: 0.15 to 0.35%, Ti: 0.05 to 0.13%, P: 0.02% or less, S: 0.02% or less, Al: 0.003 to 0.10%, N: 0.002 to 0.012%, O: containing 0.0002% or less, the balance being composed of iron and inevitable impurities, the following formula (1) is in the range of the obtained decarburized surface is less than Ac ₃ transformation point is more than 885 ℃ 859 ℃ that the performance, and the following formula (2) the maximum quenching diameter DI which is an index of hardenability performance obtained by the following more than 70mm 238mm in the range, and also the following equation (3) obtained by high-strength steel for a spring, characterized in that in the range of the indicator is tempered hardness HRC 50 or more is 55 or less that of the spring performance.
_{Ac 3 = 910-203 × √C-15.2Ni} + 44.7Si + 104V + 31.5Mo + 13.1W ... (One)
D = _{O Si} × f × DI _Mn × f f _P f _S × f × _Cu × f × f _{Ni Cr} ... (2)
HRC = 38.99 + 17.48C + 2.55Si-2.28Ni + 2.37Cr + 8.04Ti ... 3
_{However, D 0 = 8.65 × √C,} f Si = 1 + 0.64 ×% Si, f Mn = 1 + 4.10 ×% Mn, f P = 1 + 2.83 ×% P, f S = 1-0.62 ×% S, f _Cu = a 1 + 0.27 ×% Cu, f Ni = 1 + 0.52 ×% Ni, f Cr = 1 + 2.33 ×% Cr.