PURPOSE: To continuously produce the foams having a flat, beautiful surface by a method wherein, after a coated layer has been hardened, polyester film is peeled off therefrom and the coated layer is then expanded by heating.

CONSTITUTION: A base material is coated with the coating material having a heat expandable foaming agent added to the composition containing at least one kind of the compound having in its molecule at least one ethylenic unsaturated linkage hardenable by electron beam. A polyester film is then attached to the coated surface, which is then irradiated with the electron beam through the polyester film in order to harden the coated layer and the polyester film is thereafter peeled off therefrom. The coated layer is expanded by heating into a structure integral with the base plate without lowering the foaming ability, whereby the foam consisting of uniform, fine closed cells and having a flat, beautiful surface is continuously produced. As the base material, paper, synthetic resin film, nonwoven fabric, laminated wood and metal plate having a flat surface are used.