The present invention relates to a needleless injector. The needleless injector includes a piston shaft with a plurality of holders on an outer surface in a circumferential direction a cylinder assembly which slidably receives and supports the piston shaft in the forward and backward directions and a plurality of balls which are received in the cylinder assembly and disposed around the piston shaft, the plurality of balls being movable in a radial direction and inserted into the plurality of holders when the piston shaft is moved in the backward direction. The injector also includes a trigger button slidably coupled to a rear end of the cylinder assembly to form a trigger end interrupting the movement of the balls inserted into the holders in the radial direction, the trigger button releasing the interruption of the trigger end when the piston shaft is slid in the forward direction.
