There is disclosed a method of stranding together a plurality of strands (7) of sectorial cross-section around an optical fiber unit (2) which serves as a central wire material. First, a rigid type stranding machine is used to impart spiral twist to each strand (7). Subsequently, the twisted strand (7) is heat-treated to remove its strains. These strands are then fed to a planetary type stranding machine which provides planetary motion in which they make orbital rotation around the optical fiber unit (2) without making own-axis rotation, whereby they are stranded together on the optical fiber unit (2).