PURPOSE: To clean simply and easily by feeding forcibly gas or liquid from the outside of a vent hole consisting of a hole communicating the inside and outside of a mold formed on a foaming mold into the vent hole.

CONSTITUTION: A foaming mold is opened after foaming, and a foamed body is released from the foaming mold. Often a release agent is filled in a vent hole 18 or a part of foamed body is cut off and stuffed in the foamed molding 10 after the foamed body is released therefrom, and cleaning of the vent hole is required for every foaming or every several foamings. First, a gas or liquid force-feeding hose is connected with a socket 22 at the end of the hose 20 communicating with the vent hole 18, and the gas or liquid is force-fed into the vent hole 18 through the hose 20. A small piece or pieces stuffed or the release agent filled in the vent hole 18 is blown off or flowed out of the vent hole 18.