To reinforce earthquake resistance while using an existing building by additionally providing a frame having rigidity against earthquake horizontal force of the existing building on the structural plane of the outer circumferential frame of the existing building, and structurally connecting together the respective structural planes.

A frame B having rigidity against earthquake horizontal force of an existing building is additionally providing on the structural plane of the outer circumferential frame of the existing building A constituted of pillars C0..., beams G0..., and the like. This additionally provided frame B is constituted of pillars C1..., beams G1..., and the like, and the newly provided pillars C1... and beams G1... are structurally connected to the existing pillars C0... and beams G0.... In addition, it is desirable that an earthquake resistant wall and bracings are provided in the structural plane of the additionally provided frame so as to reinforce earthquake resistance. Hereby, horizontal force due to earthquake is transmitted from the existing building A to the additionally provided frame B, insufficient horizontal load carrying capacity of the existing building A is reinforced, and earthquake resistance is insured. This reinforcing work can be executed while using the existing building A.