Abstract: A roof panel is installed across and on an upper side of a plurality of horizontal members that extend in a roof lateral direction and arranged at intervals in a roof longitudinal direction orthogonal to the roof lateral direction. The roof panel includes: a frame body disposed across the plurality of horizontal members in an installed state of the roof panel; an upper heat insulation layer and a lower heat insulation layer that are supported by the frame body and are disposed side by side, one above the other; and a roof side airtight layer interposed between the upper heat insulation layer and the lower heat insulation layer, in which a thickness of the upper heat insulation layer is larger than a thickness of the lower heat insulation layer.