PURPOSE: To provide an injection molding apparatus capable of certainly cutting off a molded product and a runner by sufficiently ensuring a stroke for relaying the thrusting-out timing of a sprue lock pin to an ejector plate.

CONSTITUTION: The base end part of a sprue lock pin 21 for ejecting a runner Wr is fixed to a movable plate 18 provided in a freely liftable manner and a thrusting-out pin 18 is connected to the ejector plate 10 in a state leaving a predetermined distance (a) at the initial position of the ejector plate 10. After the ejector plate 10 is operated by the predetermined distance (a), the sprue lock pin 21 is driven so as to be thrusted out by a thrusting-out pin 15 through the movable plate 18. The spring 25 elastically energizing the return pin 25 in a return direction is provided to the return pin 25.