To eliminate an inserting fault even in the case of ensuring external appearance design property with a narrow inserting gap, by positioning a double core material in a mold, and then inserting a folding end into a skin inserting gap by sequentially taking a time difference from an outside of the material to an inside by an end treating apparatus provided in a lower mold.

After a lower core material 32 of a double core material obtained by laminating a skin 40 onto a lower mold 50 is set to a predetermined position so as to be disposed at a lower side, they are sandwiched between upper and lower molds 50 and 51, and fixed. End treating units 60 are independently provided at four sides 51a to 50d of a periphery substantially equal to a profile shape of a luggage floor trim in the mold 50, and inserting bars 61a to 61d split into four are respectively telescopically moved in cylinders 62a to 62d. That is, parts of folding ends 41 of the skin 40 set to predetermined positions and retained by the mold 51 are pressed into a skin inserting gap 38 by forwarding outside bars 61a, 61d. Then, the residues are pressed by inside bars 61b, 61c. Further, the operation is sequentially repeated to completion. And, the other sides are similarly executed.