To easily manufacutre an FRP coil spring of uniform section reduced its weight to a large extent by immersing a round string manufactured by carbon fiber of the like with a thermosetting resin for reinforcing and inserting the string through a die with a funnel-shaped drawing opening.

A round string 2 is immersed with a thermosetting resin 3 to form a reinforced round string. The round string thus formed is inserted through a die 5 with a funnel-shaped drawing opening with an injection hole approximate to the total sectional area of a reinforced fiber bundle of the resinforced round string to form an FRP yarn stock. The FRP yarn stock thus formed is coated with a crosslinking polyethylene heat-shrinkable tube (nominal size of 5.0mm), and then preliminarily heated at 80°C to shrink the heat-shrinkable tube and pressurize the FRP yarn stock. The coated FRP yarn stock is wound on a helical channel of a split mold 9 and both ends are fixed. The split mold 9 on which the FRP yarn stock is wound is left in the atmosphere of temperature of 130°C for 120 minutes while using a blowing drier.