PURPOSE: To make it possible to charge a foamed body into a structural member having an arbitrary shape without requiring perfect closing by a sealing member, etc., by introducing a bag into the structural member or the like, which bag can be inflated in conformity with the inner space of the structural member, injecting a liquidous foamable material into said bag, and allowing the material to foam.

CONSTITUTION: A balloon 5 of natural rubber or the like as a bag that is attached to the injecting end of an injector 4 is inserted, via its injection port 6, into the structural member comprising a planar panel 1 and an U-shaped panel 2 and having part attaching holes 3 in the panel 2. After a liquid foamable polyurethane raw material is injected via the injector 4, the opening of the balloon 5 is sealed, and the balloon is separated from the injector 4 to be confined in the structural member. When the foaming proceeds to a point where the foamed polyurethane raw material has a viscosity that wound not allow the material to flow outside through gaps of the structural member, the balloon 5 is exploded by a prick of needle. The foaming is continued further to fill the structural member with the foamed body.

EFFECT: The foamable material can be prevented from diffusing into the operation surrounding atmosphere, and therefore the working environment would not be contaminated.