One or a plurality of reverse-lay grooves the direction of which is inverted periodically are cut in the outer circumference of a spacer, and an optical fiber tape unit or a stack of optical fiber tape units is accommodated in this groove. The length of the diagonal lines of the optical fiber tape unit or a stack of optical fiber tape units is larger than the width and depth of a bottom portion of the groove. In the inverted portion of the groove, the normal vector of the optical fiber tape unit or the stack of optical fiber tape units points to a direction perpendicular to an opening direction of the groove in the inverted portions of the groove.
