PURPOSE: To firmly connect a temporary stage to a large column at the time when a horizontal external force works on the temporary stage, stracturally separate the large column and the temporary stage at a normal time and prevent destruction, etc., of the temporary stage by supporting the horizontal external force working on the temporary stage on the large column while allowing expansive and contractive deformation of the temporary stage.

CONSTITUTION: As a pair of jacks 16, 17 arranged to face each other between a large column 3 and a temporary stage so that one of the jacks 16, 17 works to extend by contractive motion of the other, these extending and contracting jacks 16, 17 function against expansive contractive deformation of the temporary stage as a damper to allow deformation of the temporary stage between the large column 3 and the temporary stage. In the meantime, at the time of sensing oscillation, the extensive and contractive motion of the jacks 16, 17 is stopped, the jacks 16, 17 are firmly connected the temporary stage and the large column 3 to each other and make the temporary stage supported on the large column 3 by transmitting a horizontal external force working on the temporary stage to the large column 3.