Providing a roller to prevent drag of a colorant, which is jetted on an electric wire and not dried yet, the guide roller 62 is arranged at a downstream side of a coloring nozzle 31, which jets a colorant Cm toward a highest point 3b of an outer surface of the electric wire 3 moving along a lengthwise direction thereof, in a moving direction of the electric wire 3. The guide roller 62 is formed with a pair of tapered surfaces 62b catching and supporting the electric wire 3 and approaching to each other in accordance with nearing to a rotating axis C. When a radius REW of the electric wire 3 is 1.2 mm, an angle θT formed by the pair of tapered surfaces 62b is designed at least 60 degrees and not more than θx degrees.