A sand introducing type sand molding machine is provided, wherein the apparatus produces a sand mold by leading molding sand into a molding flask or a molding space and filling the space with it by using compressed air, and controlling the pressure-variation inside the sand tank to cause it to correspond to the pattern shape by supplying the compressed air. The apparatus comprises a sand tank 1 for pressing the molding sand by the compressed air that is equipped with compressed air supplying devices to fluidize the molding sand, a communicating tube 2 that communicates with the sand tank 1, a plurality of adjusting means 5 for adjusting the pressure and flow of the compressed air that are installed in parallel, and each outlet of which is connected to the communicating tube 2, and each inlet of which is connected to the source of the compressed air 4a, an electro-pneumatic proportional valve 6, of which the supply and discharge ports are respectively connected to the source of the compressed air 4b and to the communicating tube 2, a pressure-detecting means 7 that is provided on the sand tank 1 for detecting the pressure inside it, and a controller 8 that controls the operations of the plurality of the adjusting means 5 and the electro-pneumatic proportional valve 6 that is electrically connected to the plurality of the adjusting means 5 and the pressure-detecting means 7 and the electro-pneumatic proportional valve 6.