PURPOSE: To form stably an elliptic tubular foamed product, reducing the fluctuation of its cross section-shape or dimension by foaming the product, keeping the inside thereof at the pressure equal to or lower than that of the atmosphere, when said product is extruded like cylinder by an extruder and simultaneously is foamed.

CONSTITUTION: The composition in which dichlorodifluoromethane is combined with the polyethylene with low melt index as a foaming agent, is supplied to the heat melting part 3 of an extruder 2. After the polyethylene has been melted by a screw 5, it is conveyed into a mold 5. The polyethylene composition containing a foaming agent is extruded from the inside of the mold 5 through a true circular nozzle 9 and simultaneously is foamed. Then, the primary end of a formed product 10 is closed by using a pinch, whereby the inside of the formed product is not connected to the atmosphere, and at this state it is foamed. Consequently, the elliptic tubular foamed product 11 of polyolefine family resin in which its inner wall surfaces are mutually and closly in contact and its internal cavity parts are almost diminished, may be obtained.