By stacking a plurality of short light metal billets (1), in which light metal powder has been compression-molded, inside a long container (2) having an internal diameter (D) that is larger than the external diameter (d) of the short light metal billets (1) and applying pressure to the same inside the long container (2) at a temperature higher than normal temperature to compress the same until the external diameter becomes equal to the internal diameter (D) of the long container (2), the interfaces (4) between the short light metal billets (1) are joined as a result of friction.