A steel for a high-strength bolt that includes from 0.50 mass % to 0.65 mass % carbon, from 1.5 mass % to 2.5 mass % silicon, 1.0 mass % or more chromium, 0.4 mass % or less manganese, greater than 1.5 mass % molybdenum, 0.03 mass % or less phosphorus and sulfur combined, and balance iron and inevitable impurities.