PURPOSE: To aim at the automation of building and joining of column reinforcing steel by holding new column reinforcing steel with a holding device, moving it with a vertical conveyor and a horizontal conveyor and building it on the existing column reinforcing steel, then joining an interval between two main reinforcements of those of column reinforcing steel by means of a joining coupler.

CONSTITUTION: After a new column reinforcing steel cage is held by a holding device A, this holding device A is moved upward of a structural body 26 along a rail 4 by a vertical conveyor, and connected to a horizontal conveyor B being on standby in a rail 30 at one end of a temporary ceiling 29. Next, the conveyor B is moved along the rail 30, and the new cage is roughly positioned on top of the existing cage locked to a slab 39. Subsequently, fine adjustment is carried out by movements in all directions by a connecting part 35 of the conveyor B and rotation by an alignment conducting part 38, thereby elongating an inner pipe of a double pipe of this conducting part 38, and then a main reinforcement 43 is held by claws of an arm 10 and both load directions of both these main reinforcements 11 and 43 are accorded with each other, thus permanent positioning takes place. A joining coupler 28 loosely attached to the main reinforcement 11 is crushed by claws of an arm 9 and both these main reinforcements are joined together.