PURPOSE: To contrive a cost reduction by a large margin by a method wherein a vane member is fitted and narrowly supported on a sliding-contact guide to be made rotational running along a shaft member which is inserted centering in the vane member, and the vane member is continuously applied a welding while being extended by desired pitches to automatically obtain a finished product.

CONSTITUTION: A screw shaft member 3 is inserted in the center of the screw vane member 1 previously applied a continuous molding in a spiral-shape, the shaft member 3 is rotated with its one end fixed and also the vane member 1 kept fitted and narrowly supported on the sliding-contact guide 17 is made rotational running along the shaft member 3 to continuously be applied a welding while being extended by desired pitches. Whereby the modling operations are not necessary to be applied to a large number of the screw vane member 1, nor welding operations are required to be applied between the vane members 1 each other. Further, the screw vanes continuously molded can be cut is desired lengths for the use, the operations are remarkably simplified and the cost is also reduced in large.