Medicament delivery device comprising - a generally elongated housing comprising two housing parts having distal and proximal ends, a proximal part and a distal part; - a medicament cartridge comprising a proximal opening closed by a septum, an axially movable distal stopper, and a first enclosure wherein a liquid and a gaseous fluid are enclosed; - a medicament delivery member attachable to said proximal part and having a non-delivery end; - a medicament cartridge holder wherein said medicament cartridge is coaxially arranged, said cartridge holder being arranged coaxially movable inside said proximal part and comprising holding means (38, 40) capable of holding said medicament cartridge holder in a non-activated position in which said cartridge holder is releasebly engaged to said proximal part and in which a predetermined distance is present between the septum and the non-delivery end; characterized in that said device further comprises - a manual pressure mechanism comprising the housing parts (10, 12) and a static plunger rod which is arranged between said distal stopper and the distal end of said distal part; wherein said manual pressure mechanism is arranged to be moved from a non-pressure position in which said housing parts (10, 12) are coaxially and movably connected to each other and said plunger rod is abutting said distal stopper to a pressure position in which said housing parts (10, 12) are inwardly moved in relation to each other such that the plunger rod is moved into the medicament cartridge causing a pressure build-up inside said enclosure; and - an activation mechanism arranged to interact with said holding means (38, 40) only when said manual pressure mechanism (10, 12, 44) is in the pressure position for disengaging said cartridge holder from said non-activated position to an activated position in which said cartridge holder is axially displaced said predetermined distance whereby said septum is penetrated by the non-delivery end and the liquid is expelled due to the pressure built inside the enclosure. - a generally elongated housing comprising two housing parts having distal and proximal ends, a proximal part and a distal part; - a medicament cartridge comprising a proximal opening closed by a septum, an axially movable distal stopper, and a first enclosure wherein a liquid and a gaseous fluid are enclosed; - a medicament delivery member attachable to said proximal part and having a non-delivery end; - a medicament cartridge holder wherein said medicament cartridge is coaxially arranged, said cartridge holder being arranged coaxially movable inside said proximal part and comprising holding means (38, 40) capable of holding said medicament cartridge holder in a non-activated position in which said cartridge holder is releasebly engaged to said proximal part and in which a predetermined distance is present between the septum and the non-delivery end; characterized in that said device further comprises - a manual pressure mechanism comprising the housing parts (10, 12) and a static plunger rod which is arranged between said distal stopper and the distal end of said distal part; wherein said manual pressure mechanism is arranged to be moved from a non-pressure position in which said housing parts (10, 12) are coaxially and movably connected to each other and said plunger rod is abutting said distal stopper to a pressure position in which said housing parts (10, 12) are inwardly moved in relation to each other such that the plunger rod is moved into the medicament cartridge causing a pressure build-up inside said enclosure; and - an activation mechanism arranged to interact with said holding means (38, 40) only when said manual pressure mechanism (10, 12, 44) is in the pressure position for disengaging said cartridge holder from said non-activated position to an activated position in which said cartridge holder is axially displaced said predetermined distance whereby said septum is penetrated by the non-delivery end and the liquid is expelled due to the pressure built inside the enclosure.