PURPOSE: To reduce the development of gas deffect, such as blow hole, and to cast a sound casting by reducing the pressure in a cavity through a hollow part by a pressure reducing device after pouring a prescribed quantity of molten metal into a tundish, opening a nozzle and casting the molten metal in the tundish into the cavity.

CONSTITUTION: A gas permeabile mold 1 is carried to a pouring station with a carrying device and a suction hole 17 from the pressure reducing device 12 is brought into close contact with the hollow part 11 in the gas permeable mold 1. Then, a stopper 13 is brought into close contact with a nozzle 14 and the molten metal is poured into the tundish 15 from the ladle 4. Successively, after killing the molten metal in the tundish 15, the stopper 13 is risen with a stopper rising/lowering means 16 and the nozzle 14 is an opened to execute the casting into the cavity. After solidifying the cast steel in the gas permeable mold 1, the mold is shaken out to obtain e.g. a cylindrical thin casting with a flange. As the result, the pouring speed of the molten metal is fast and the molten metal is difficult to disturb and the entrapment of the air and slag is little and the development of the casting defect is eliminated.