An inclined coil spring has a core wire 10 made of steel with a pearlite structure; and a copper plating layer 20 formed of copper or a copper alloy and covering an outer peripheral surface 11 of the core wire 10. The steel contains 0.5 mass% or more and 1.0 mass% or less carbon, 0.1 mass% or more and 2.5 mass% or less silicon and 0.3 mass% or more and 0.9% by mass or less of manganese, the rest being iron and inevitable impurities. The copper plating layer 20 has a crystallite size of 220 ± 50 Å.
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