A method of manufacturing a coil spring using a helicoid reduction mill includes supplying a coil spring material linearly unrolled by a prestraightener to a surface treatment machine and then short-blasting or scarfing its outer surface to surface-treat the coil spring material; primarily heating the surface-treated coil spring material to a predetermined temperature using a first heater; sequentially supplying and pressurizing the primarily-heated coil spring material in a stepwise fashion such that the coil spring material has the same diameter as that of a coil spring to be manufactured; measuring the diameter and the length of the coil spring material and then cutting the coil spring material to a desired size; secondarily heating the cut coil spring material to a predetermined temperature using a second heater; forming the secondarily heated coil spring material into a coil spring using a coiling machine; and oil-quenching and then tempering the formed coil spring.