A needleless pain-free injection device according to the present invention comprises: a valve body; a valve member provided in an internal space of the valve body and having an outer circumference that airtightly slides along the inner wall of the valve body; a liquefied gas container which communicates with the internal space of the valve body and which has one end thereof detachably coupled to the valve body and has an open nozzle unit formed on the other end thereof; an operating knob provided on the end of the valve member that is exposed from the valve body; a cylinder body coupled to one side of the valve body and having an internal space in the longitudinal direction; a piston member provided such that one end thereof can slide in the internal space of the cylinder body, and having a piston rod provided from the one end; an injection liquid unit provided with an injection liquid piston rod coupled to the piston rod; and a gas flow passage forming means for selectively establishing and blocking the communication of the valve body and the cylinder body with the outside air.
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