One or more optical fiber elements each constituted by a coated glass fiber are fed to an over-coating device and an over-coating is applied to the optical fiber elements in a lump, the feeding speed of the optical fiber elements to the over-coating device is made larger than the take-up speed of the over-coated optical fiber onto a take-up reel so as to give longitudinal compression strain to the glass fibers of the over-coated optical fiber. The glass fiber has compression strain of not less than 0.03% to less than 0.10% in a longitudinal direction thereof at room temperature.