A method to efficiently make flaskless upper and lower molds that are stacked, to efficiently spray a release agent in a closed space, and to promptly place a core. The method includes the steps of holding a match-plate between one pair of cope and drag flasks that are horizontally positioned, each of them having a sand-filling port for supplying molding sand at its side wall, defining upper and lower molding spaces by inserting upper and lower squeeze-plates in respective openings of the pair of cope and drag flasks which openings are opposed to the match-plate, putting the pair of cope and drag flasks and the match-plate in a vertical position, and causing the sand-filling ports to be placed in an upper position, spraying a release agent into the two upper and lower molding spaces, supplying molding sand through the sand-filling ports to the two upper and lower molding spaces, and squeezing the molding sand in the two upper and lower molding spaces.