Needleless syringe

A needleless syringe comprising:

• a tubular casing having a mounting portion at the tip end thereof that can be used to mount a liquid container which includes:
• a container and a plunger for pushing the liquid contained in the container out of a nozzle;
• a piston that is provided in the casing and can reciprocate in the axial direction of the casing;
• a gas supply portion that is provided behind the piston at the rear end of the casing, and supplies gas to move the piston toward the tip end of the casing;
• an airtight space provided between the piston and the gas supply portion;
• a valve mechanism that opens and closes the gas supply from the gas supply portion to the airtight space;
• a pressing member that is provided ahead of the piston in the casing and is capable of reciprocating axially in an axical direction thereof and is driven by the piston driven by the gas pressure in the airtight space, and has a plurality of pressing surfaces whose positions in the axial direction are stepwise different from each other;
• a pressing surface changing mechanism that drives the pressing member to change the pressing surface each time the pressing member is driven back;
• a gas release mechanism that releases the gas that remains in the airtight space outside the casing each time a pressing operation of a fixed stroke is completed,
• wherein the pressing member contacts the plunger of the liquid container mounted in the mounting portion on the pressing surface thereof, and after pressing the plunger towards the tip of the casing for the fixed stroke in conjunction with the piston's forward movement, the plunger is returned.