To efficiently manufacture a coated optical fiber and an optical fiber tape without losing the transmission characteristics of the coated optical fiber and the optical fiber tape.

At least one kind of electron ray hardenable resin composition is applied to a bare optical fiber core wire, and the resin composition is hardened by electron ray irradiation so that a single layer or multi-layer resin coated optical fiber can be manufactured. In this case, the electron ray hardenable resin composition includes 10-90 wt.% urethane(meth)acrylateoligomer (A) and 10-90 wt.% reactive diluent (B). As for the electron ray irradiation, the accelerating voltage of electron rays is set to be 50 kV 150 kV (a), and a distance between the electron ray exit of an electron ray irradiating device and a coated optical fiber surface is set to be ≥0.5 mm and <10 mm (b), and an irradiating atmosphere is nitrogen or helium at an atmospheric pressure (c), and the concentration of oxygen in the atmosphere is set to be 1,000 ppm or less (d), and the coated optical fiber is irradiated from at least two directions.