Abstract: A cartridge magazine for a firearm comprises a case having a guiding extrusion extending downwardly along at least one wall therein selected from a front wall and a rear wall, a bullet support provided inside the case so as to move up and down and including another guiding extrusion to be movably inserted in the guiding extrusion at a portion selected from a front and a rear portion thereof and having a balance protrusion at another portion thereof, and a spring for elastically and constantly supporting the bullet supporting means. The cartridge serves to smoothly send bullets loaded therein toward a powder chamber of a firearm while maintaining a horizontal level of the bullet support.