To provide the joint of a heat-insulating roof panel, in which heat-insulating performance is not damaged in the joint and sure moisture resistance is ensured and which also has excellent workability.

The water upper side of a heat-insulating roof panel 1B on the water lower side is covered with an end section on the water lower side of a U-shaped sectional connecting member 4 and the end section of the water lower side of the connecting member 4 is fixed. An end section on the water upper side of the connecting member 4 is inserted to a section, from which a heat-insulating material 3 is removed, at an end section of the water lower side of a heat-insulating roof panel 1A on the water upper side. The heat-insulating roof panels 1A, 1B on the water upper side and the water lower side are fixed onto beam members 10, and the connecting member 4 and the heat-insulating roof panel 1A are fastened. A foamable resin material 8 is injected from the filler hole 5 of the connecting member 4, the connecting member 4 is filled, and a cover 6 is closed. The foamable resin material 8 is cured with the resin material 8 fast stuck on the end sections of the heat-insulating materials 3 of the heat-insulating roof panels 1A, 1B and metal plates 2a, 2b, through the slits 7a, 7b, 7c of the connecting member 4, and an integral heat-insulating roof panel, in which the heat-insulating materials are sandwiched by the metal plates, is formed.