Safety syringe of the type for use with a hypodermic needle where, after the use of the syringe to inject medication from its drum, the needle separates from the distal end of the syringe and retracts into the syringe barrel, thus avoiding punctures accidental after use, which includes: a. a syringe drum (43, 443, 643)； b. a needle (37, 437, 637) disposable disposed at the distal end of the syringe (20, 420, 620)； C. a plunger (48, 448, 648) axially movable in the drum (43, 443, 643) and having a withdrawal lumen (39, 439, 639) open at its distal end to receive the needle (37, 437, 637) after the use of the syringe, a piston seal (40, 440, 640) provided at the downstream end of the plunger in sliding engagement with an internal cylindrical wall surface (33, 433, 633) of the syringe drum ( 43, 443, 643)； d. The lumen (39, 439, 639) is sized to receive sufficient combined length of the needle (37, 437, 637) and the needle port seal (41, 441, 641) that, after removal, the needle (37, 437, 637) is entirely in the syringe (20, 420, 620), and the needle (37, 437, 637) then remains in the retracted position, characterized by the fact that: e. a needle port seal (41, 441, 641) for needle engagement (37, 437, 637) near its proximal end and carrying the needle (37, 437, 637) to the lumen (39, 439 , 639) during needle withdrawal (37, 437, 637), the needle port seal (41, 441, 641) that has a distal support surface against which the gas under pressure can rest, the seal of the needle port (41, 441, 641) frictionally coupled with the inner wall of the piston lumen (39, 439, 639) and movable in the piston lumen under gas pressure to retract the needle (37, 437, 637) in the lumen (39, 439, 639)； F. a gas release cell (25, 425, 625) located in the syringe assembled distally of the plunger (48, 448, 648) between the needle port seal (41, 441, 641) and the distal end of the drum (43 , 443, 643), intact and inoperative before the substantial completion of the drug injection by movement
