To provide a structure and method for reinforcing an existing structure, which join a reinforcing material and the existing structure by forming the tough joint between the existing structure and the reinforcing material using a very tough adhesive without containing a causative agent of a sick house syndrome.

The tough joint formed using the very tough adhesive is interposed between a frame 12 of the existing structure 11 containing an existing concrete structure and the reinforcing material 21 inserted and disposed in the frame 12, so as to join them together. Force is transmitted while properly allowing the relative displacement between the reinforcing material 21 and the existing structure 11 by making the maximum relative displacement (distortion) δmax2 large although the maximum strength (τmax2) being small, whereby local destruction in the existing structure 11 and the reinforcing material 21 can be avoided and the force can be transmitted by the entire boundary surface to draw out 100% of resistance of the reinforcing material 21.