PURPOSE: To simply and exactly perform alignment, positioning and adjustment of right and left guide rails in a short time by providing a rail holding mechanism and aligning gages far apart from each other.

CONSTITUTION: Since a rail holding mechanism 15 and aligning gages 16 are provided far apart from each other, right and left guide rails 3 are held at first using only the rail holding mechanism 15 so that they are held a specified distance apart, and their inclination is adjusted, and in this state, the whole of the right and left guide rails 3 can thus be moved and adjusted to be positioned at a rough position. During this operation, since the aligning gages 10 are not mounted, contact of aligning reference lines 5 with the aligning gages is prevented, and the swing and offset of the aligning reference lines 5 do not occur. Thus, without requiring the useless time required to eliminate the swing and offset of the aligning reference lines 5, the guide rails are smoothly and finely adjusted to the vertically hung down, aligning reference lines 5 while the aligning gages 16 are attached to the positions suitably apart from the rail holding mechanism 15, and the right and left guide rails can thus be aligned, positioned and adjusted respectively.