PURPOSE: To provide an assembling construction method excellent in site workability and labour saving and a working support for it.

CONSTITUTION: Elevating hooks (B) and working supports (A) equipped with their driving sources are installed in a parallel state at a working site as several sets (A1-L), (A2-L), (A3-L), (A1-R), (A2-R), (A3-R) on which the elevating hooks face against each other, and horizontal reinforcement support bars 40 are engaged between the elevating hooks (B) facing against each other free to disengage respectively. A stirrup (a) is leaned against the reinforcement support bar 40 in a lowering state of the elevating hook (B), and after an upper side main reinforcement (b) inserted through the stirrup (a) is placed on the reinforcement support bar 40, the elevating hook (B) is raised to specified height unanimously, and the stirrup (a) in a state hanging down from the upper side main reinforcement (b) is bound on the upper side main reinforcement and a lower side main reinforcement, and thereafter, the reinforcement support bar 40 is removed from the elevating hook B.