PURPOSE: To remove the strain applied to a foam in forming just after a die and consequently obtain foam, in which strength is favorably balanced, by a method wherein foam is once formed and, after being passed through a high temperature atmospheric furnace, the free foaming of the foam is promoted and the resultant foam is stretchingly formed with rolls provided at the outlet of the furnace.

CONSTITUTION: Synthetic resin and additional matter, which are fed from a hopper and mixed with foaming agent on their way, are mixed and melted under high pressure and high temperature by means of a screw so as to be fed in an extruder and, after that, cooled down to the foamable resin viscosity region and then fed to a die. By releasing the melt from high pressure region to low pressure region at the die 1, the melt is formed by a forming mold 2 and first rolls 3 into sheet-like foam having the desired cross-sectional shape. The resultant foam is passed through a furnace, which is equipped with a hot air generating device 6 so as to be able to set its temperature within the range of 100 - 160°C, so as to apply stretching force to the reheated foam by second rolls 4 by controlling their speed under the condition that the strength balance is controlled in order to obtain the foam. The temperature in the furnace is set within the temperature range, which is higher than the softening point of the foam and satisfies the condition that no breakage of cell due to the melting of the surface of the foam occurs, and preferably set to 105 - 160°C.