To uniformly, efficiently and continuously make a running thin wire irradiated with an electron beam which has been difficult conventionally and to cope with faster speed of wire drawing, without impairing the transmission characteristic of optical fibers, when an electron beam irradiating apparatus for thin wires is used in the manufacture of optical fibers.

An electron beam irradiating apparatus for thin wires has an electron beam irradiating section, having openings where thin wires run, an electron beam generating section equipped with an electron-generation means, an electron-accelerating means and an electron focusing means and a communicating section, which allows the electron beam generating section to communicate with the electron beam irradiating section. The electron beam irradiating apparatus includes at least a single-stage differential evacuation means for keeping the pressure in the electron beam generating section lower than that in the electron beam irradiating section. The electron beam irradiating apparatus has thin wires, which run through the openings and continuously pass through the inside of the electron beam irradiating section are irradiated with the electron generated from the electron generating means by way of the communicating section between the electron beam generating section and the electron beam irradiating section after the electrons are accelerated by the electron acceleration means and are focused by the electron focusing means.