PURPOSE: To ease the inflow of molten metal, prevent fins and improve working efficiency by applying coat only in the engraved grooves for casting.

CONSTITUTION: After coat 7 is applied over the entire surface of one 1 of a pair of molds, the coat 7 of the other portions is scraped off by using a scraper or the like, leaving the casting groove 2 portions. The other mold opposing to the one mold 1 is also treated in the manner similar to the above. Next, when the both molds are butted, the occurrence of minute clearances 7' as for conventional molds is obviated because of the absence of the coat on the mating surfaces. Thence, when a force- exhaust hole 5 is connected to a suction device and air is removed, the residual air in the casting groove spaces is removed from the venting fine groove around the casting grooves 2, whereby negative pressure is developed. When molten metal is poured at this time, the flow into the casting grooves becomes good and the casting may be done surely.