PURPOSE: To constitute a composite core material so that adhesion of a panel material to the composite core material is made easy and reliable and the panel material is not loosened after adhesion, by a method wherein a porous core material is pressed into a resin foam through a pressing-in surface of the resin foam so that the porous core penetrates through the resin foam.

CONSTITUTION: In a porous core material 3 which is molded of paper into a honeycomb state, a rubber adhesive agent is applied to an inside end surface 7 of the porous core material 3 pressed into a resin foam 1 and pressed into the resin foam 1 through a pressing-in surface 2 of the resin foam 1. In this case, the porous core material 3 is pressed into the resin foam 1 until the porous core material 3 is penetrated through the resin foam 1 by making use of a matter whose height H is higher than a height h of the resin foam 1 and an outside end surface 5 of the porous core material 3 is exposed on the pressing-in surface 2 of the resin foam 1. Since powder of the resin foam 1 does not adhere to the outside end surface, a panel material (such as a colored steel sheet or a plastic sheet) is stuck reliably to the same outside end surface 5.