PURPOSE: To simplify an operation, and to provide excellent external appearance even when fibers are buried in parallel in organic glass by stretching one yarn strand of a linear state by sequentially bridging it in a plural-strands parallel state between first and second guide wheels by a relative movement.

CONSTITUTION: When a plurality of yarns are stretched in parallel by using a yarn stretching apparatus, a bridge member 5 is first moved along guide rails 6, a movable guide wheel 2 is moved to a position for holding a straight line for connecting a right slit 4 to a left slit 4 between stationary guide wheels 1, a yarn strand 3 is passed through the slits 4, and stretched between positions A and B. Then, after the member 5 is moved in a reverse direction, the strand 3 is suitably pulled at the positions A, B to bridge the strand 3 in a tensile state of a zigzag manner between the wheels 1 and 2, and a plurality of parallel strands 3 are stretched by an equal tension in an opening 7 of an apparatus body 8.