PURPOSE: To provide a tube bending method of generating no reduction of thickness at the outer surface side of the tube at the time of bending the tube.

CONSTITUTION: A wire 6 having elongation resistance and flexibility in the bending direction so as to make the stress of the outer surface of a tube P almost zero while withstanding the elongation action on the outer surface of the tube P which is apt to generate at the time of bending the tube is fixedly held on the projectingly bent outer surface of the tube P or on the side a little outside the outer surface over the bending working range of the tube P from one end to the other end thereof through end part clamp mechanisms 3L.3R and an intermediate clamp mechanism 5. Then, by applying the bending moment by a pair of hydraulic cylinders 75 over the bending working range of the tube P from one end to the other end thereof, bending is executed by applying the compression force from the outer surface toward the inside of the tube P in the axial direction of the tube P.