Injection apparatuses are known as an apparatus that injects a molding material into a mold and fills the mold with the molding material to form a desired product. As in the injection apparatus disclosed in Patent Document 1, for example, recent injection apparatuses apply actuating force to an injection cylinder by using an electric motor. The injection apparatus of Patent Document 1 includes an injection cylinder device for actuating an injection plunger to inject a molding material into a mold, and a conversion cylinder device for supplying hydraulic oil to the injection cylinder device. In the injection apparatus of Patent Document 1, an electric motor is used as the driving source to drive the conversion piston of the conversion cylinder device when supplying the hydraulic oil to the injection cylinder. In the injection apparatus of Patent Document 1, therefore, the driving force of the electric motor actuates the conversion piston of the conversion cylinder device to supply the hydraulic oil to the injection cylinder device, and then the supplied hydraulic oil actuates the injection piston of the injection cylinder device in the direction in which the molding material is to be injected.