PURPOSE: To simply manufacture the tapered tube without necessitating large external force by using a hollow extruded stock whose waveform part is continued in the lengthwise direction, and compressing or expanding the waveform part so that length in the peripheral direction of the waveform part is varied continuously in the lengthwise direction of the extruded stock.

CONSTITUTION: At the time of manufacturing a hollow extruded stock whose cross section is square, it is extruded by forming waveform parts 2a- in which a ring part is varied by continuing alternately a recessed part and projecting part of a mountain shape, in each side part 1a- of the upper and the lower parts and the left and the right in a hollow cross section. Subsequently, compressive force is imparted so that length in the peripheral direction (width direction) of the waveform parts 2a- is varied continuously in the lengthwise direction of the hollow extruded stock. By deformation of the waveform parts 2a- of each side part 1a of the upper and the lower parts and the left and the right, cross sectional dimensions of the minimum compressive force imparted part of the extruded stock, and cross sectional dimensions of the maximum compressive force imparted part become maximum and minimum, respectively, and the hollow extruded stock is formed to a tapered tube A whose cross sectional dimensions are varied continuously and proportionally extending from one end side in the lengthwise direction to the other end side.