To closely fill a heat insulating material by mutually joining/filling a granular fibrous heat insulating material to/in a reverse side space of a wall face material surrounded by a frame body by an adhesive.

In a manufacturing method of a heat insulating inner wall panel 1, a wall face material 3 is installed on one side of a frame body 2 to be horizontally arranged. An air-blown granular fibrous heat insulating material 4 and an atomized liquid adhesive 41 are simultaneously sprayed on and filled in a reverse side space of the wall face material 3 surrounded by the frame body 2, and after flatly finishing the surface by properly leveling the surface, the adhesive 41 is solidified by heating and drying. In the heat insulating inner wall panel 1, the inner wall face material 3 such as a gypsum board is installed on one side of the wooden frame body 2 assembled in a square shape, and the granular fibrous heat insulating material 4 is mutually joined by the adhesive 41 to be filled in the reverse side space of the inner wall face material 3 surrounded by the frame body 3. Thus, the heat insulating material is closely filled, a defect of heat insulating performance is eliminated, and since a blowing-in heat insulating material and a wall panel can be integrally handled, handling on work is facilitated.