PURPOSE: To apply printing to the surface of a porous body, by such a simple method that a pattern to be printed is formed on an almost colorless transparent heat-meltable film from a light absorbable coloring material and the film is closely adhered to the surface of the porous body such as a foam and the pattern is allowed to generate heat by the flash irradiation of the porous body on the film to be fusion-bonded to the surface of the porous body.

CONSTITUTION: A line picture pattern 3 to be printed on a plastic foam 1 such as foamed styrol or polyurethane foam is formed on a heat-meltable base film 2 from light absorbable ink and the pattern forming surface of the film 2 is closely adhered to the foam 1. When the porous body is subjected to flash exposure on the film 2 using a flash lamp, the light absorbable ink forming the patter 3 absorbs light to allow the pattern 3 to generate heat and the base film of the heat generating part is melted to be fuse-bonded to the surface of the foam along with the ink. A non-pattern part holds a film shape and, when said part is removed as a unnecessary part, a desired pattern is left on the foam.