To conduct earthquake-resistant execution easily and rapidly by installing brace-shaped earthquake-resistant reinforcing members to a plurality of opening sections formed so as to be faced to the outer circumferential surface of an existing building respectively.

Grooves 8 are prepared to joint surfaces 7 formed to the outer circumferential surfaces of the end-section crossed sections of adjacent brace sections 6, 6, and anchors 11 are driven to the slabs 3a of stair landings 3 in the upper and lower sections of an opening section 4 and left-right wall surfaces 10. Shear cotters 12 are arranged to the head sections of the anchors 11, brace units 5 are hung into the opening section 4, and sections among the grooves 8 of the joint surfaces 7 of the unit 5 and the cotters 12 are filled with a grouting material 13. Consequently, the existing building 1 is reinforced in an earthquake-resistant manner and aseismicity is improved, the consent of residents is easy to be obtained by reinforcing the opening sections 4 of each stair landing 3, and earthquake-resistant reinforcing works are designed and executed easily. Accordingly, vertically continued columnar reinforcing bodies are formed by the brace units 5, 5 by intalling these brace units 5, 5, and earthquake- resistant reinforcement can be conducted efficiently.