To make it possible to exactly insert optical fibers into grooves.

A housing die 58 is a member for peeling away the groove holding members 10e of a spacer 10 and inserting the coated optical fibers 50a into the spiral grooves from which the groove holding members 10e are removed. The outer peripheral side thereof is provided with a plurality of take-up bobbins 68 of the groove holding members 10e circumferentially rotating in synchronization with the rotation of the spiral grooves and delivery bobbins 7O of the coated optical fibers 50a in correspondence to the number of the spiral grooves. This housing die 58 has a die body 58a, a peeling die 58b, a fiber insertion guide 58c and a fiber assembling die 58d. The die body 58a is a hollow cylindrical member opened at both ends and the insertion 58e of the spacer 10 is formed through the center of its longitudinal axial direction. The bore of this insertion hole 58e is made slightly larger than the outside diameter of the spacer 10 and is supported freely rotatably via bearings 58f.