In a resin sandwich panel, the two resin skin material sheets have peripheral edge portions thereof joined to each other so as to form an internal hollow portion. The resin core material is disposed in the hollow portion. At least one of surfaces of the resin core material opposing the two resin skin material sheets has a groove portion extending across the entire surface, and a depression communicating with the groove portion. At least one of the two resin skin material sheets additionally has an atmosphere-opened through-hole provided in a thickness direction thereof. When the one of the surfaces of the resin core material and the corresponding resin skin material sheet are surface-to-surface adhered to each other in the hollow portion, air between the surfaces and the skin material sheet is guided to the depression via the groove portion, and exhausted out of the atmosphere-opened through-hole.