PURPOSE: To eliminate a large-scale apparatus such as fork lift by a method wherein retaining parts are so arranged to allow relative passage of an extension nut downward while blocking the relative passage thereof upward at a plurality of upper and lower points being separated and a releasing mechanism is provided to release the retention with the retaining parts freely.

CONSTITUTION: A bolt 1 set upright at an attitude vertical or along the vertical way is so arranged to be retained freely on an extension bolt 4 added thereto being erected at the lower part thereof and on an extension nut 5 used at a link part thereof. Retaining parts 6 adapted to allow relative passage of the extension nut 5 downward while blocking the relative passage thereof upward are arranged at a plurality of upper and lower points being separated while a releasing mechanism 7 is provided to release the retention with the retaining parts 6 freely. This eliminates the need for a large-scale apparatus such as forklift.