Abstract: In a conventional method of impregnating die-cast articles, the sealing property is not excellent due to air being dragged into the sealant.In the present invention, the dragging of air into the sealant is prevented by adjusting the pressure of the sealant storage vessel and the pressure of the impregnation vessel to substantially the same level and then flowing the sealant from the sealant storage vessel into the impregnation vessel. After impregnation, the sealant reenters the sealant storage vessel, and pressure is applied to the die-cast articles so as to remove excessive sealant from them.