a method of and an apparatus for shaping a hollow blank member by a forging operation is provided . the interior of a hollow blank member is filled with a liquid pressure medium which is enclosed therein in sealed condition . an external pressure is applied to the hollow blank member , and the pressure of the pressure medium is maintained as an internal pressure which opposes the external pressure , and part of the pressure medium is discharged externally while applying a desired plastic deformation to the hollow blank member .