PROBLEM TO BE SOLVED: To provide a waterproof structure of an external floor with a high external heat insulation performance, for which a process is not easily affected by weather even when an adhesion method is used and management of an adhesive is facilitated.SOLUTION: In a waterproof structure 1 of an external floor 2, a heat insulation material 11 is brought into direct contact with an underfloor 4. Even in the state that the underfloor 4 is wet immediately after rainfall for instance, by providing heat insulation materials 11, 12 on the underfloor 4, a layer above the heat insulation materials 11, 12 is not affected by the wet underfloor 4. The process is not easily affected by weather in the adhesion method for which a waterproof sheet 20 is bonded. Further, by fixing the heat insulation materials 11, 12 and a heat insulation material pressing plate 13 to the underfloor 4 by fixing machine screws 16, the need of an adhesive is eliminated when fixing the heat insulation materials 11, 12 and the heat ins
