To prevent stress corrosion cracking by reducing residual stress generated at a bent product in a large radius bending of an aluminum alloy hollow extruded shape material.

A metallic shape material 1 is excessively bent in one direction by first press bending, and thereafter bending-back is carried out in an opposite direction by second press bending, and a bent shape (bending height) to be a target is obtained. A push-in amount S of a bending die of the second press bending is adjusted corresponding to a deviation amount Δd(=d1-d0) from a reference value d0 of the bending height d1 after the first press bending. The correspondence relation of the deviation amount Δd and the push-in amount S by which a bending height to be a target is obtained through the second press bending is preliminarily obtained as an initial setting of conditions before start of mass production. The deviation amount Δd is measured after the first press bending about the respective metallic shape materials after the start of the mass production, and bending is carried out in a push-in amount S determined based on the corresponding relation in the second press bending.