To easily manufacture a tapered tube of small diameter by repeating the condition where the diameter of a cylindrical die for forming is reduced while a cylindrical tube is pressed in the axial direction to the cylindrical die for forming, and a condition where the diameter is enlarged.

A tube P is interposed between a jig 21 and a tapered cylindrical die 4. An advancing/retracting core 5 which is continuously provided on an output shaft of a second hydraulic cylinder 3 is reciprocated at the prescribed timing under the condition where the thrust in the axial direction is given to the tapered cylinder die 4 side. When the advancing/retracting core 5 is advanced, the diameter of the tapered cylindrical die 4 is increased by the taper fitting effect of the advancing/retracting core 5 to the tapered cylindrical die 4 and the effect of a first slit and a second slit. A part on a tip side of the cylindrical tube P is expanded. When the advancing/retracting core 5 is retracted, the diameter of the tapered cylindrical die 4 is reduced, and fitting of the cylindrical tube P to the tapered cylindrical die 4 becomes deeper. When advancement/retraction of the advancing/retracting core 5 is repeated, increase/ reduction of the diameter of the tapered cylindrical die 4 is repeated, and the tapered range is increased.