Safety syringe, comprising a housing for receiving a cartridge holder, a cartridge holder slidably mounted within the housing, the cartridge holder having a distal end mounting a needle and an open proximal end for receiving a cartridge, a cartridge received in the cartridge holder, the cartridge being filled with a medically active substance and being movable in the cartridge holder between a distal position and a proximal position, the cartridge being closed at a distal end by a closure member, the closure member being piercable by the needle upon movement of the cartridge into a distal position, a plunger rod extending into the housing, the plunger rod having at a distal end a first engagement means for engaging an inside surface of the cartridge and for pushing the piston distally, the first engagement means being designed to be moved proximally relative to the cartridge only upon a minimum pulling force being exerted on the plunger rod, a first locking means on the cartridge holder and a second locking means inside the housing, the first and second locking means cooperatingly and automatically locking the cartridge holder upon move-ment of the cartridge holder in its distal position, the first and second locking means being designed to allow the cartridge holder to be moved from its distal position into its proximal position upon exertion of a proximally directed pulling force on the plunger rod which is less than the minimum pulling force.
