PURPOSE: To obtain an extrusion formed product having a skin layer from a kind of foam resin by a metal mold for foam resin extrusion forming by such an arrangement wherein an opening which is gradually expanded in funnel shape toward its outlet is formed in an internal resin passage piercing through the center of a mandrel arranged in a resin flow passage.

CONSTITUTION: When foam resin flowed into a passage 5 moves into a funnel-shaped opening 6, it becomes decompressed condition and it begins foaming and flows out. On the one hand, when foam resin flowed into an outer passage 16 passes through an outer passage slit 4, it becomes such a condition wherein it is hard to foam, since it is applied with the pressure of foaming of resin flowing out of the funnel-shaped opening 6 and its interior becomes a foam core 17, and a foam extrusion formed product A of which surface layer becomes a skin layer 18 of low foaming rate is obtained. To give glossiness to the outer surface of this product, a covering resin is extruded into a resin passage 2 through an extrusion machine 13 for covering resin and a covering resin extrusion slit 10 simultaneously with the foam molding of the product. By this method, a foam extrusion formed product having a foam core and a skin layer each of which differs in foamed condition from the other can be obtained by using one kind of foam resin and the construction of a metal mold can also be simplified.