PURPOSE: To manufacture a stable hollow polyoxymethylene unstretched body, the outer diameter, inner diameter and surface condition of which are uniform, at high productivity by a method wherein a land ratio at the tip part of a double die is held at a constant value within a specified range.

CONSTITUTION: In a method of obtaining a hollow polyoxymethylene unstretched body by continuously extruding molten polyoxymethylene from between the dies of a double die consisting of an outer die 13 with an indirect cooling part 4 therein and an inner die 11 having a pressure fluid supplying port at its center and, after that, by bringing the polyoxymethylene into direct contact with refrigerant, the hollow polyoxymethylene unstretched body is manufactured under the condition that the land ratio at the tip part of a double die is held at a constant value within the range of the land ratio of 10W300. The land ratio denotes the ratio of the length (l) of the lands of a part over which the inner diameter D of the outer die and the outer diameter (d) of the inner die are constant to the gap (t) between the lands at the tip part of the double die. If the land ratio is smaller than 10, no stable forming is effected and the outer and inner diameters of an unstretched body flactuate violently and high speed super-stretching can not be realized. If the land ratio exceeds 300, the cutting-off of an unstretched body occurs and stable continuous forming can not be realized.