To execute a high quality bending without developing buckling and strain on the surface plate of a metal-made hollow shape material, to enlarge bending range, to simply execute a partial bending and to reduce the working manhours by refrigerating the metal-made hollow shape material to freeze water in a bag, forming an insert of the ice in the hollow part and bending.

The vinyl bag 4 applied with a water leakage preventing treatment with a vinyl sealer is inserted into the hollow part 3 at the bending part 2 of the aluminum-made hollow shape material 1. This vinyl bag 4 has the cross section of the same as or larger than the cross section of the hollow part 3 and is inserted to the part which does not receive the deformation caused by bending near the bending part 2. The opening hole of the vinyl bag 4 is closed with a fastening tool 5 of a rubber, etc., after filling up the water into the inserted vinyl bag 4, and refrigerated, and the water in the vinyl bag 4 is freezed to form an insert 6 of the ice. Under condition of the water freezed in the vinyl bag 4, the bending part 2 of the aluminum-made hollow shape material 1 is bent with a jig.