To provide a floating floor structure that prevents the deterioration of a waterproof sheet due to rainwater and the rust and degradation of a member such as a supporting frame and ensuring a waterproofness for a prolonged term by doubling a waterproof structure in the floating floor structure in a sheet waterproof construction method using a floor finishing plate, and also that improves reliability on a fixing to a waterproof foundation for the supporting frame and being capable of reducing a construction cost.

In the floating floor structure, the waterproof sheets 2 made of a thermoplastic resin are laid and arranged on the waterproof foundation 1, and the supporting frames 3 consisting of pedestals 31 and bolts 32 erected from the pedestals and covering the pedestals and the lower parts of the bolts with the thermoplastic resin are fixed to the waterproof foundation at specified places on the waterproof sheets made of the thermoplastic resin. In the floating floor structure, the pedestals for the supporting frames are covered with lining-increasing sheets 5, and the lining-increasing sheets, the waterproof sheets made of the thermoplastic resin and the pedestals for the supporting frames are welded. In the floating floor structure, panel receivers 6 are screwed to the bolts for the supporting frames, composite panels 8 having welding resin layers 81 on surfaces are fixed to the panel receivers and sections among the adjacent composite panels are waterproofed.