PURPOSE: To form molded goods of which the main parts are formed of thin parts by injection molding to molded goods having dense metallic structures which are free from gas inclusion and mis run and having a high strength.

CONSTITUTION: A correlation between the thickness for obtaining the defectless molded goods and the packing amt. F necessary for the inside of a cavity indispensable for packing of laminar flow is recognized by previously executing the observation of the flow behavior in the cavity and the verification of the molding test of a flat plate casting test piece by using transparent plastic models and thereafter, the injecting and packing is executed at an ultra-low speed of 0.1 to 0.5m/s of an initial gate speed V. The injecting and packing are executed at an ultra-high speed of 60 to 360m/s until completion of the packing after the necessary packing amt. is attained.