PURPOSE: To adjust the opposite interval of one pair of board guide rails so as to be variable while the parallelism of the rails are being maintained satisfactorily by a simple mechanism utilizing a wire.

CONSTITUTION: The following are installed in the title apparatus: a fixed board guide rail 3 which is fixed to a base stand 1; a movable board guide rail 4 which is parallel to the fixed board guide rail 3, whose opposite interval is made variable and which is supported by the base stand 1; and reference pins 41, 42 which position a board supported between the fixed and movable board guide rails 3, 4. In addition, the title apparatus is provided with the following: a wire 15, for guide rail movement, which is fixed to the movable board guide rail 4 in a plurality of parts and which is stretched and laid on the side of the base stand in such a way that a plurality of fixation points are moved to the same direction; and a driving pulley 16 which runs and moves the wire 15 for guide rail movement.