An injection molding apparatus of plastic material including a mold, a fixing plate of the mold, a distributor of the plastic material to be injected and a plurality of injectors connected to the distributor and each including a valve pin controlled by a respective rotary electric motor and a transmission. The fixing plate has a cavity facing the mold on a first face, within which the distributor is contained, and each electric motor with the relative transmission is housed, in a quickly insertable and removable manner, within a respective seat arranged on a second face of the fixing plate opposite to the first face, laterally with respect to the corresponding injector.