An injection apparatus for a combined member of a constant-velocity joint boot comprising: a base mold which includes at least one elevation cylinder and characterized in that the base mold has a purging block mounted on a rod of the elevation cylinder to be elevated by operation of the elevation cylinder; and a core mold which includes a molding part upwardly protruding through an inner area of the purging block of the base mold, a sprue mounted at a central point of a flat upper surface to allow a melt resin material to be supplied, a plurality of runners radially mounted around the sprue to extend to the molding part, and injection gates mounted at end portions of the runners to form an injection structure for the melt resin material, wherein the runners is downwardly inclined in the direction of the injection gates and the injection gates are located at an upper area adjacent to a parting line interposed between an outer peripheral surface of the molding part of the core mold and an inner peripheral surface of a large-diameter tube body of a boot; and a support mold which includes a pair of slide molds (41a, 41b) moving forward and backward in a horizontal direction by a hydraulic cylinder or other driving means so as to engage with each other or be separated from each other, and support grooves (42a, 42b) respectively formed inside the slide molds to grasp the outer peripheral surface of a lower end portion of a bellows connection tube and the outer peripheral surface of the large-diameter tube body; and a sealing cover which is mounted at the central portion and has a cover hole upwardly dented so as to accommodate a small-diameter tube body and the bellows connection tube which are disposed at the upper part; and an injection mold which is mounted above the support mold, vertically ascends and descends by the hydraulic cylinder or other driving means to come into contact with the support mold or to be separated from the support mold, the injection mold having an injection bushing which vertically crosses the central portion of the cover hole of the sealing cover so as to supply the melt resin material through an injection hole of the injection bushing. a base mold which includes at least one elevation cylinder and characterized in that the base mold has a purging block mounted on a rod of the elevation cylinder to be elevated by operation of the elevation cylinder; and a core mold which includes a molding part upwardly protruding through an inner area of the purging block of the base mold, a sprue mounted at a central point of a flat upper surface to allow a melt resin material to be supplied, a plurality of runners radially mounted around the sprue to extend to the molding part, and injection gates mounted at end portions of the runners to form an injection structure for the melt resin material, wherein the runners is downwardly inclined in the direction of the injection gates and the injection gates are located at an upper area adjacent to a parting line interposed between an outer peripheral surface of the molding part of the core mold and an inner peripheral surface of a large-diameter tube body of a boot; and a support mold which includes a pair of slide molds (41a, 41b) moving forward and backward in a horizontal direction by a hydraulic cylinder or other driving means so as to engage with each other or be separated from each other, and support grooves (42a, 42b) respectively formed inside the slide molds to grasp the outer peripheral surface of a lower end portion of a bellows connection tube and the outer peripheral surface of the large-diameter tube body; and a sealing cover which is mounted at the central portion and has a cover hole upwardly dented so as to accommodate a small-diameter tube body and the bellows connection tube which are disposed at the upper part; and an injection mold which is mounted above the support mold, vertically ascends and descends by the hydraulic cylinder or other driving means to come into contact with the support mold or to be separated from the support mold, the injection mold having an injection bushing which vertically crosses the central portion of the cover hole of the sealing cover so as to supply the melt resin material through an injection hole of the injection bushing.