PURPOSE: To bend a pipe without generating creases or causing flattening in bending the pipe by winding the pipe on a bender performing bending while pressing the bent part of the pipe from inside.

CONSTITUTION: The tip of a pipe 1 is fixed to a bender 3 by a clamping die 4, and the pipe 1 is bent by rotating the bender 3 and the clamping die 4 in the direction of the arrow in cooperation with a mandrel 12. At this time, as the circumference of the bent part of the pipe 1 subjected to compressive force is in close contact with the bender 3, inside of the pipe 1 is projected due to buckling. Therefore, a urethane rubber bag 7 is expanded by supplying pressure oil into the rubber bag 7. The projected part is pressed back by a pressing piece 10 to prevent buckling. Accordingly, bending of a pipe having a bent part of small diameter, or a pipe having small thickness compared with the diameter can be carried out without generating creases.