PURPOSE: To reduce the manufacturing cost of a hollow stock in which the maximum length of a cross section is large.

CONSTITUTION: To an extrusion process for forming annular extruded stocks 11a, 12a whose cross sectional shape is annular by extruding a metallic stock billet through a die, and at least two points opposed in cross sections of the annular extruded stocks 11a, 12a, extension force for extending an outline shape of the cross section of its annular extruded stocks 11a, 12a is imparted. In such a way, a hollow stock is manufactured by two processes of an extension process for forming hollow stocks 11b, 12b having a cross sectional shape of the maximum length being larger than the maximum length of the cross sections of its annular extruded stocks 11a, 12a.