To provide a new roof structure which can effectively discharge moisture lifting to a roof according to change of the temperature environment inside and outside a building, without providing a venting layer or a ventilation layer.

According to the roof structure, a heat insulation layer 11 is arranged immediately above a roof skeleton layer 10 formed of lightweight cellular concrete, and a moisture conditioning layer 13 is arranged over the heat insulation layer 11, followed by arranging a waterproof layer 14 immediately above the moisture conditioning layer 13. The heat insulation layer 11 has imparted thereto moisture resistance by which a volume of water, equal to or lower than a moisture capacity of the moisture conditioning layer 13 is permeable, and the moisture conditioning layer 13 has imparted thereto moisture absorbing/desorbing characteristics which exhibit almost the same equilibrium water content in the course of a moisture absorbing procedure and a moisture desorbing procedure.