PURPOSE: To easily form connecting heads of double rolled pipes which will not allow any leaking, by installing a plural number of parallel grooves along the outer circumference within a limited width at the end part of double rolled pipes, and then, by swelling out the parallel grooves to become a bridge.

CONSTITUTION: On the outer circumferential surface 1' at the straightened end part of a double rolled steel pipe 1 having a depressed part 8 at the rolled end margin, a plural number of parallel grooves 2 which have a saw-toothed cross section and which are parallel to the direction of circumference of the pipe, are installed within the area having a relatively narrow width with a rotary edge member 5. Then, the pipe 1 is fixed by a chuck 6 and a bridge-shaped swelled out head part in which the parallel grooved part 2 becomes a pushing seat face 3, is formed at the end of the pipe, by pushing the pipe 1 from the outside of the end with a punching member 7. In this way, because the depressed part 8 at the seat face 3 is cut into pieces bythe parallel grooves 2 and, at the same time, the depressed part 8 will be crushed by the saw-toothed face when this pipe is connected to another pipe by means of screw, a pipe connection which will not allow any leaking from the depressed part 8 can be performed.