To receive outer force by a brace structure itself, perform economical, sure and safe earthquake-proof reinforcement, relieve an existing building from proof stress burden by extremely decreasing joint points and prevernt inconvenience for the building by enlarging openings.

A major assembly brace structure is formed out of brace materials 1 arranged over the plural stories of a building, laterally mounting materials 2 mounted under floors at existing beams in stories or under the existing beams and column materials 3 mounted along existing columns to perform earthquake-proof reinforcement of an existing building. The brace materials 1 and structural members around floor penetrating ports in stories on their way are integrated with reinforcing bars or cotters and concretes to transmit horizontal force at stories on their way to the members of the large assembly brace structure.