An injection molding apparatus has a barrel for conveying a molten substance, a screw, a first base for supporting the barrel, a power unit, a second base for supporting the power unit, links, a motor, a screw driver, a plurality of injection guide links, and an injection connecting plate. The first base is threadedly secured to the bed. The barrel has one end secured to the first base. The power unit is fixed on the second base. The links each have one end connected to the first base and the other end connected to the second base. The screw driver between the bases is moved under the guidance of the injection guide links. The injection guide links penetrate through the second base, having one end secured to the screw driver with the injection connecting plate provided in the second base. The injection connecting plate is pivotably secured to the power unit. These features are adopted to the deformation caused by heat, and provide a closed loop of force, isolation of deformation, and a modular design that is particularly suitable to high speed injection molding.