Abstract: An improved injection molding apparatus having a fixed mold 7 having a molten resin passage 16b and a movable second mold 8 having a molten resin passage 18 is presented in which residual hardened resin left in molten resin passages of the injection apparatus is removed automatically after every injection operation. The invented device is provided with a reciprocating member 34 which is coupled in molten resin passages 16b, 18, and during the injection step, the molten resin passage 16b is extended to the molten resin passage 18 by moving the reciprocating member 34 into the second mold to communicate a mold cavity 17 with a resin injection device 14. After the completion of the injection step, the reciprocating member 34 is moved to the back position to remove any resin left in the molten resin passage towards the first mold.