To uniformly and efficiently pack a crushed material in a method for producing a sandwich panel having strength and heat insulating- soundproofing performance by packing a crushed waste material of a hard foamed synthetic resin in the spaces of a sandwich panel.

For the stabilization of the packing density of a crushed foamed synthetic resin 4 in the spaces of the sandwich panel, a honeycomb material 3 having closed cell structure is used as a base material for a core and the packing amount and packing density of a foamed packing material 4 are fixed. For the easiness of packing in a cell space and a measure against the static electricity of the crushed foamed material which is a problem in terms of uniform packing and work efficiency, an antistatic agent of a surfactant is mixed/ sprayed in/to the crushed foamed material. For the adhesion of the sandwich panel, a two-pack expandable urethane adhesive or an epoxy resin adhesive producing a thick adhesive layer is used.