To provide a double floor structure which prevents warping and torsion of substrates, exerts high soundproofing performance, and has excellently fixed upper face plates, to thereby reduce plate squeak, and to provide a method of constructing the double floor structure.

The double floor structure is formed of a plurality of support legs 1 which are erected from a building foundation such as a concrete slab, the plurality of rectangular substrates 2 arranged on the support legs side by side, and the upper face plates 3 arranged on the substrates 2 so as to be orthogonal to a long side of each substrate 2. The support legs 1 are arranged at locations corresponding to long side edges of the substrates 2 at intervals almost equal to a plate width of each upper face plate 3. The substrates 2 fixed to the support legs 1 thus arranged are free from overall warping and torsion, and proof against formation of small warping and torsion which are prone to occur due to the overall warping and torsion, to thereby ensure the horizontality of the entire body of the substrates 2.