It is an object to realize and establish new extrusion technology for manufacturing a light-metal hollow member (product) having excellent mechanical properties with constant stability and also efficiently manufacturing the product having a strength satisfying a required level at low cost, by using a hollow die such as a bridge die. The object is achieved by dividing and joining/welding a light-metal material with a hollow extrusion die and then extruding the light-metal material to form in a desired cross-sectional shape through a die opening, wherein the strain level applied to the light-metal material after the joining/welding is maintained at 1.8 or more and the extrusion is performed.