To improve productivity, to reduce parts cost and manufacturing cost, to reduce the weight of a car body, and to prevent the stress of a shock load or a fatigue load from concentrating on a part between a plastically deformed part and an original shape keeping part when the shock load is applied to them.

This is a cylindrical front side member 10 for constituting a car body frame 1 and has a shock absorbing part 11 which is plastically deformed when it receives an axial shock load and an original shape keeping part 12 which is integrally formed with the shock absorbing part 11 continuously in the direction of the length thereof and nearly keeps an original shape when it receives the axial shock load. Thickness of a part connecting the shock absorbing part 11 to the original shape keeping part 12 is gradually changed and the thickness T1 of the original shape keeping part 12 is made larger than the thickness t1 of the shock absorbing part 11.