PURPOSE: To accurately bend pipes without giving any damge to the pipes, by detecting the location of a mandrel and by feeding back the detected signal to a loaction regulating mechanism through a controller when a pipe, into which a mandrel rod having the mandrel is inserted, is bent with a pipe bender.

CONSTITUTION: A pipe 1 is fitted on a mandrel 2 set to the front end of a mandrel rod 3, and the pipe 1 is held by a bending frame 6 and a clamp 7. Then, a shifting plate 16 is moved along a guide rod 15 through a regulating nut 17 by manually rotating a screw rod 18, and the clearance between a bending start point and a bending work point C is adjusted to become zero. After the adjustment is performed, a controller 23 is switched to a automatic operation mode and a transmitting body 12 and a receiving body 13 are set to an operation- start state. Since a contact frictional force is generated between the inner surface of the pipe 1 and the mandrel 2, the location of the mandrel is detected by the transmitting body 12 and the receiving body 13 when the mandrel rod 3 is extended, and the bending work point and the bending start point of the mandrel 2 are harmonized by retreating the mandrel 2 under the control of the control device 23, when the bending is performed, an accurate bending is performed without giving any damage to the pipe 1.