To provide a sill tightening structure making it possible to easily adjust a sill in its vertical direction and easily and rapidly correct the inclination of a dwelling house.

The sill tightening structure comprises a foundation 1 constructed of concrete, a sill 2 laid on top of the foundation 1, a gate-shaped upper fitting 3 covering the top of the sill 2, lower fittings 4 secured to both sides of the foundation 1, and sets of bolts and nuts 5 consisting of bolts 5a and nuts 5b for fastening the upper fitting 3 to the lower fittings 4. The sets of bolts and nuts 5 are operated from the sides of the sill 2 to interpose foundation packing 6 between the foundation 1 and the sill 2 and adjust the height of the sill 2.