PURPOSE: To increase the strength of a screw joint as well as to enable a thread to be cut in such a way that the thread parallel portion of a thin wall steel pipe is left thick by using four tool blocks each of which holds a chaser having two ridge cutting edges.

CONSTITUTION: A thread is cut at the end portion of a steel pipe while tool blocks 5 holding chasers 4a fitted on each die-head are being rotated. In this case, each chaser 4A is constituted to be of two ridge cutting edges, and four sets of tool blocks 5 are disposed symmetrically around the die-head. By this constitution, a thread can be cut in such a way that a parallel portion at the tip end of the thread section of a thin wall steel pipe is left thick, and thereby a screw joint can be increased in strength. As a result, pipe end swaging works and the like can be eliminated, consequently, a proposed method contributes much to cost reduction.