It is an object of the present invention to provide a novel aluminum tube of an oval cross section that has a wider range of applications and added values. A disk-shaped metal slug (21) is impact-extruded with the use of a die (14) and a punch (13) each having an optimally designed structure to form a metal tube (T) integrally including a mouth, a shoulder and a body of an oval cross section. A hem portion of the oval body of the tube (T) thus formed and hardened by the impact extrusion is once deformed into a circular shape, and then trimmed off by a turning operation.