To provide a sill reinforcing structure which can connect a sill to a continuous footing so as to exert sufficient tensile resistance without cutting a wall at all and without boring the continuous footing.

A reinforcing member 1 for use in the sill reinforcing structure is composed of a top plate 2 and a side plate 3 extending from the top plate at right angles, and is formed like an almost L-shaped figure in cross section. The top plate 2 and the side plate 3 have an L-shaped stiffening rib 4a erected along one-side edges thereof, and an L-shaped stiffening rib 4b erected along other-side edges thereof. Further each corner at which the top plate 2 and the side plate 3 abut on each other has arranged a corner rib 5 thereon. The sill reinforcing structure 11 is constituted by abutting and bonding the rear surface of the side plate 3 to the indoor side surface of the continuous footing 12 and abutting and bonding the rear surface of the top plate 2 to an upper bed of the sill 13.