To provide a manufacturing method of a hollow double wall panel, in which the hollow double wall panel having only one gloss side can be efficiently blow-molded.

This hollow double wall panel is manufactured by blow-molding an amorphous resin. Only one side of the hollow double wall panel has gloss. A mold clamping is performed by arranging the amorphous resin parison 7 between a pair of split molds 5 and 6, and, one mold 5, of which the wall having a not glossy surface of the panel is formed, out of a pair of the split molds 5 and 6 is heated up to a temperature X, lower than the thermal deformation temperature of the amorphous resin, and to the same time, the temperature of the other mold 6, of which the wall having a glossy surface is formed, is set to a temperature A lower than the thermal deformation temperature at the mold clamping. While the temperature of the other mold 6 is being held at temperature B, which exceeds the thermal deformation temperature after the mold clamping, lower than the temperature X of the one mold by 5-20°C, the mold releasing is effected at temperature C, lower than the temperature X of the other mold, that is, X-C=5-20°C.