To provide an aluminum alloy-made cylinder body and a method of manufacture thereof lightening weight also improving pressure resistance strength.

In a cylinder body 1, one end part has a closed cylindrical shape, in its peripheral surface, a plurality of rib-shaped protruded parts 8 extended in a circumferential direction is formed. This cylinder body 1, using a casting mold provided with a rib-shaped recessed part, is manufactured by casting. Then, by a synergetic effect of a mechanical reinforcing effect by the rib-shaped protruded part 8 and a strength improving effect by fining of a composition, the cylinder body 1 excellent in pressure proof strength light in weight can be obtained.