The present invention provides a liquid medicine injection apparatus capable of injecting an additional fluid after completion of injection of a liquid medicine. The liquid medicine injection apparatus capable of injecting an additional fluid after completion of injection of a liquid medicine according to one embodiment of the present invention includes a cylinder elongated in a direction and having a nozzle formed at one end of the cylinder； a piston installed to be hermetically movable within the cylinder in the direction, wherein the piston defines a liquid medicine storage space to be filled with the liquid medicine introduced through the nozzle； an injector provided at the other end of the cylinder to allow the piston to be moved； a fluid tank for storing a fluid in a sealed state, wherein the fluid tank is disposed in the cylinder so as to be movable together with the piston and is deformable by a pressure； a needle unit disposed between the nozzle and the fluid tank, wherein the needle unit can penetrate a portion of the fluid tank to communicate the nozzle with the fluid tank； and a cap member provided between the needle unit and the fluid tank and deformable to allow the needle unit to penetrate the fluid tank.
