A computer controlled electric syringe includes: a piston unit including a piston being configured to press and move a rubber plug of a cartridge by a second end to discharge a medicinal solution from a cartridge through an injection needle； a ball screw having a screw shaft and a nut portion that is screwed into the screw shaft, the screw shaft being loosely inserted into the hollow portion of the piston through the opening, the nut portion being coupled to the piston； a screw shaft supporting portion rotatably supporting the screw shaft of the ball screw； a rotation preventing portion configured to prevent the nut portion of the ball screw from being rotated； and a piston supporting portion supporting the piston to be movable in an axial direction of the screw shaft along with the nut portion by the rotation of the screw shaft.
