It is an object of the present invention to suppress a coating resin from being shaved off in an event where optical fibers are sent out from a coating dice. When a Young's modulus of ultraviolet curable resins 13 located on outermost layers of optical fibers 3 is 300 MPa or more, and the Young's modulus is 300 MPa to 600 MPa, a plurality of the optical fibers 3 in which friction force measured by the following measurement method is 0.3 N or less are arranged in parallel to one another, these respective optical fibers 3 are fixed to one another intermittently along a longitudinal direction thereof, and adhered portions 5 are formed. A ring 30a is formed of an optical fiber specimen 30, an end portion 30b on one end side of the optical fiber specimen 30 is inserted into the ring 30a so as to make a knot, and a contact portion 30d in which portions of the resin are brought into contact with each other is formed. In this state, the respective end portions 30b, 30c on both sides of the ring 30a are grasped and pulled in a direction of being spaced apart from each other, and friction force between the portions of the resin at the contact portion 30d at this pulling time is measured.