Anti-seismic reinforcement and expansion method for building and anti-seismically reinforced and expanded building

A method of expanding a mid-rise building to a high-rise building, where a quake-absorbing foundation (5) for a high-rise building is newly provided outside the foundation of an existing mid-rise building (1), support members (6) are stood on the newly provided quake-absorbing foundation, and new dwelling floors (10) are fabricated above the existing building using the support members. After the completion of the new dwelling floors, upper floors of the existing mid-rise building are dismantled and removed and remaining individual floors of the building are remodeled sequentially. Thus, with the dwellers living in the building, a mid-rise building can be expanded to a high-rise building having excellent quake-resistance.