PURPOSE: To form a true circular flare at the tube end by inserting a tapered mandrel into the tube end rotating a cylindrical member, and at the same time, pressing the outer peripheral face by a roller.

CONSTITUTION: After mounting a cylindrical tube member 1 to the chuck 3 of a lathe, a mandrel having taper for forming flare of specified shape is pressed into the tube end of the cylindrical tube member 1 by a tail stock 4. Then, a roller 6 is attached on the tool rest of the lathe slanting it to match the roller face 6a to the finished taper of the flare part formed at tube end of the cylindrical tube member 1. Under this condition, the roller 6 is thrusted against the tube end of the tube member 1 while rotating the chuck 3 of the lathe. The tube end is stretched by pressing force between the mandrel 5 and roller 6 and spread radially. At this time, by moving the roller 6 in the direction of the arrow and further pressing the mandrel 5 in, a true circular flare part having specified taper is formed at the tube end of the tube member 1.