(57) A high-strength spring steel which produces retained austenite less than 10 % in content by weight after quenching in steps of quenching tempering, and has high fatigue strength and relaxation resistance. The steel contains 0.30 to 0.75 % carbon, 1.0 to 4.0 % silicon, 0.5 to 1.5 % manganese, 0.1 to 2.0 % chromium, and 2.0 % or less nickel, all by weight, and iron and unavoidable impurities for the remainder. The steel further contains 0.05 to 0.5 % vanadium and/or 0.05 to 2.0 % molybdenum, as required. Preferably, the retained-austenite content is set to less than 10 % by restricting the carbon, silicon, and nickel contents as follows: 35 × C (%) + 2 × Si (%) + Ni (%) < 23 %. Preferably, moreover, the oxygen and nitrogen contents of the steel are restricted to 0.0010 % or less and 0.005 % or less, respectively. By doing this, the fatigue strength of the steel can be further improved.