A needleless pain-free injection device according to the present disclosure includes a valve body, a valve member provided in an internal space of the valve body and airtightly sliding along the valve body, a liquefied gas container communicating with the internal space of the valve body and detachably coupled, at one end thereof, to the valve body, an operating knob provided on the exposed end of the valve member, a cylinder body coupled to one side of the valve body and having an internal space, a piston member provided such that one end thereof slides in the internal space of the cylinder body and having a piston rod, an injection unit provided with an injection piston rod coupled to the piston rod, and a gas passage forming means for selectively establishing and blocking the communication of the valve body and the cylinder body with outside air.
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