PURPOSE: To prevent the generation of a wrinkle or a deformation by inserting into a hollow part of a hollow shape to be made to an outer circumferential side in bending with a core metal whose clearance against the hollow part is larger in a specific value comparing to a core metal inserted in a hollow part to be made to an inner circumferential side.

CONSTITUTION: A hollow shape 1 having plural numbers of hollow parts 2, 3 is bent by respectively inserting core metals 14, 15 in the hollow parts. In the hollow part 3 of the hollow shape 1 to be made to an outer circumferential side, the core metal 15 whose clearance against the hollow part is 0.3-1.0mm larger in comparing to the core metal 14 inserted in the hollow part 2 to be made to an inner circumferential side is inserted. Further, in the hollow part 3 of the hollow shape to be made to the outer circumferential side with bending, the core metal composed of a material with more elasticity comparing to the core metal inserted in the hollow part 2 to be made to the inner circumferential side is inserted. In such a way, the generation of a wrinkle or a deformation in the bending time of the hollow shape can be prevented and the bending method of the hollow shape which improves the productivity can be obtained.