A piercing mechanism for piercing a cartridge (10) comprises a cartridge container (20) adapted to receive and hold a cartridge (10) and allow a movement of the cartridge (10) from a start position via a piercing state to an end position, the cartridge (10) comprising a septum (14) covering a dispensing port (15) and a piston (12) adapted to be moved from a proximal position along an axial direction of the cartridge (10) to a distal position, a hollow needle (30) having a distal end (31) and a proximal end (32), the hollow needle (30) being immovably fixed in the piercing mechanism and adapted to pierce the septum (14) with the proximal end (32) when the cartridge (10) is moved from the start position via the piercing state to the end position, a plunger (40) adapted to cause the movement of the piston (12) when the plunger (40) is moved from a first position to a second position, wherein the second position is closer to the hollow needle (30) than the first position, and a spring mechanism (50) adapted to be compressed by the movement of the cartridge (10) from the start position to the end position, wherein the spring mechanism (50) protrudes with regard to the proximal end (32) of the hollow needle (30) when the plunger (40) is in the first position.
