Abstract: A plurality of grooves are formed in an outer surface of a spacer. The grooves are formed continuously in the longitudinal direction by a die which surrounds the circumference of the spacer. The grooves extend, in the form of parallel periodically reversing helices along the longitudinal direction of the spacer. The optical fibers are guided into the grooves through guide plates arranged to rotate in a reciprocating motion about the spacer. The position of the grooves is detected and converted into an electric signal. The operation of an actuator for driving the movement of the die and the guide plates is controlled on the basis of the electric signal thereby rotating the plates and the die in synchronism with displacement of said grooves.