An injection molding machine having a simple structure and adapted to quickly produce molded products without significant flaws on the surface is provided. It comprises a plunger being adapted to introduce the molten metal into the cylinder section, a nozzle for injecting the molten metal fed from the plunger into a metal mold and a piston arranged within a cylinder section of the plunger to slidingly reciprocate. It includes a piston drive unit for driving the piston to slidingly reciprocate, a stopper member for controlling the retracted position of the piston drive unit and a position selecting unit for defining a projected position and a retracted position for the stopper member.