A positioning of a plurality of optical fibers 11 is performed by a pair of position regulating members 12a and 12b. Then, the paired position regulating members 12a and 12b are moved along two guide members 13, 13 in such a manner as to have a predetermined distance therebetween. A ribbon support member 15 is placed between the paired position regulating members 12a and 12b in such a way as to support the optical fibers 11. The plurality of optical fibers 11 are held and fixed by the holding members 17a and 17b. Further, the plurality of optical fibers 11 put on the ribbon support member 15 are sandwiched by the ribbon support member 15 and the pressing tool 19 opposed thereto. In a terminal portion structure 110a of a ribbon fiber 10, terminal portions of optical fibers 102 are arranged horizontally in parallel, an adhesive tape is stuck onto at least one of upper and lower surfaces of at least the terminal portions.