In a mould (1) with vertical parting surface, each mould cavity (2, 2') is connected through a wide throat with its own after-feeding reservoir (3, 11). When the mould (1) has been poured, a gas pressure is applied through a duct (15, 19) to a metal surface in the after-feeding reservoir (3, 11). This gas pressure is not allowed to exceed the metallostatic pressure in the mould at the surface, at which the pressure is applied, until the metal in the ingate (4) has solidified or the ingate has been blocked in some other way. At the location where the duct (15, 19) opens into the after-feeding reservoir, it is covered by an element (16, 20) that is impermeable for the metal having been poured but permeable for the pressurized gas. When the metal in the ingate (4) has solidified or the ingate has been blocked in some other way, the gas pressure may be increased.