An injection molding apparatus comprising: a mold including a lower-side mold and an upper-side mold forming a cavity with the lower-side mold; a vertical injection cylinder having a nozzle in a lower end, to which stick-shaped molding materials are sequentially supplied in line from the upper side; a heating means; and a push-in means including a push-in shaft pushing the stick-shaped molding materials downward in the injection cylinder; characterised in that: an upper-side mold attachment board having a two-layer structure, in which a thick upper-layer is made of iron and occupying most of the upper-side mold attachment board and a thin lower-layer portion is made of epoxy glass having a good heat insulation property is provided, the upper side mold attachment board having a through hole with a nozzle such that heat is only transmitted from the injection cylinder to the mold through contact between a flat end surface of the nozzle and an upper surface of the mold; and the heating means is configured to generate a temperature gradient in which the temperature increases from above to below inside the injection cylinder, thus changing sequentially the molding materials supplied in the injection cylinder from solidification to a completely molten state; wherein, the molding material in a middle level is in a half-molten state in which the lower side is molten, thereby filling the space in the cylinder body forming an air-tight stopper, such that when the stick-shaped molding material in the highest level is pushed by the push-in shaft, the molding material in the middle level pushes, as a piston, the completely molten molding material in the lowest level, thereby injecting the completely molten molding material into the cavity. a mold including a lower-side mold and an upper-side mold forming a cavity with the lower-side mold; a vertical injection cylinder having a nozzle in a lower end, to which stick-shaped molding materials are sequentially supplied in line from the upper side; a heating means; and a push-in means including a push-in shaft pushing the stick-shaped molding materials downward in the injection cylinder; characterised in that: an upper-side mold attachment board having a two-layer structure, in which a thick upper-layer is made of iron and occupying most of the upper-side mold attachment board and a thin lower-layer portion is made of epoxy glass having a good heat insulation property is provided, the upper side mold attachment board having a through hole with a nozzle such that heat is only transmitted from the injection cylinder to the mold through contact between a flat end surface of the nozzle and an upper surface of the mold; and the heating means is configured to generate a temperature gradient in which the temperature increases from above to below inside the injection cylinder, thus changing sequentially the molding materials supplied in the injection cylinder from solidification to a completely molten state; wherein, the molding material in a middle level is in a half-molten state in which the lower side is molten, thereby filling the space in the cylinder body forming an air-tight stopper, such that when the stick-shaped molding material in the highest level is pushed by the push-in shaft, the molding material in the middle level pushes, as a piston, the completely molten molding material in the lowest level, thereby injecting the completely molten molding material into the cavity. an upper-side mold attachment board having a two-layer structure, in which a thick upper-layer is made of iron and occupying most of the upper-side mold attachment board and a thin lower-layer portion is made of epoxy glass having a good heat insulation property is provided, the upper side mold attachment board having a through hole with a nozzle such that heat is only transmitted from the injection cylinder to the mold through contact between a flat end surface of the nozzle and an upper surface of the mold; and the heating means is configured to generate a temperature gradient in which the temperature increases from above to below inside the injection cylinder, thus changing sequentially the molding materials supplied in the injection cylinder from solidification to a completely molten state; wherein, the molding material in a middle level is in a half-molten state in which the lower side is molten, thereby filling the space in the cylinder body forming an air-tight stopper, such that when the stick-shaped molding material in the highest level is pushed by the push-in shaft, the molding material in the middle level pushes, as a piston, the completely molten molding material in the lowest level, thereby injecting the completely molten molding material into the cavity.