To enhance the ease and smoothness of releasing of a resin molding and realize the releasing of the resin molding without deforming (or distoring) the resin molding by a method wherein the number of releasing ejecting parts to the resin molding is increased.

At the back of a core mold 23, an ejecting plate 28, which can be pushed towards a cavity 38 by means of a pushing-out rod 27 pushed out by an eject cylinder, is arranged. At the same time, a cylinder 32 is fixedly supported onto the ejecting plate 28. At the same time, a sleeve piston 30 is connected to the actuating shaft 33 of the cylinder 32 so as to push the sleeve pin 30 by means of the driving force of the cylinder 32 in order to compress a boss part 39. After that, a resin molding is released with the pushing force of the sleeve pin 30 by means of an extruder.