A method of manufacturing an internal grooved tube according to the present invention
includes the steps of inserting a grooved plug into a blank tube rotatably, and
then pressing the blank tube against the outside surface of the grooved tube with
several balls revolving both around the circumference of the blank tube and on
its axis in location of the grooved plug inserted, while drawing out the blank
tube longitudinally in one direction, wherein the number of balls is limited to
2 to 3. A lead angle of the grooves to the tube axis is preferably limited
to 26 to 45 degrees.
