PURPOSE: To prevent ununiform voids from generating by a method wherein support (a) comprising liquidproof and air permeable sheet stacked with another air permeable sheet, support (b) with the same constitution as the support (a), and stock solution of expandable resin are expanded and cured in a shaping device.

CONSTITUTION: The stock solution 3 of the expandable resin consisting of phenolic resin in resol stage, blowing agent, and acid curing agent is cast from a mixer-stirrer 5 on the support (a) comprising the liquidproof and air permeable sheet 1 piled with the air permeable sheet 2. The support (b) with the same constitution as the support (a) is fed parallel to the support (a). Furthermore, the supports (a) and (b) and the stock solution 3 of the expandable resin are continuously moved so as to pass through the shaping device 6 in order to be expanded and cured in the shaping device 6. After that, the air permeable sheets 2, which constitute the supports (a) and (b), and separated from the supports (a) and (b) respectively, resulting in obtaining the phenolic resin foam 4.