PURPOSE: To cast under pressure a defectless casting having no shrinkage cavity without a riser in sand mold gravity casting of a cast iron casting by casting the cast iron while pressing the wall of a casting mold in the mating surface direction.

CONSTITUTION: A cast iron is cast to a casting product part 4 in a casting sand mold by a gravity casting method as shown in the figure. At the same instant, a pressure P is exerted on mold walls 1, 1 thereof preferably perpendicularly to respective mating surfaces 2 to prevent the movement of the walls 1, 1 in the initial period for solidification of the molten metal. The pressure in this stage is selected usually within a range of 0.5W100kg/cm2 although said pressure varies with casting conditions such as the amt. of casting, etc. The pressing means in this stage may be any, for example, means of pressing a fluid pressure cylinder or placing load on the casting mold. The casting mold and above all the sprue system thereof are different from the same in the prior art and the method of this invention is executed on the precondition that the mold is so devised as to solidify the molten metal earlier in the charging route such as a gate, flow-off or the like than in the product part thereof.