A drug injection device is disclosed. A drug injection device, according to the present invention, comprises: a plunger which is connected to an ampoule filled with an injectable solution and applies pressure to the injectable solution in the ampoule； a manual plunger handle which is connected to one side of the plunger and manually applies pressure to the plunger； and an automatic plunger pressurizing unit which is selectively connected to the plunger in a position adjacent to same and automatically applies pressure to same by means of power.
