A medicament injection device comprising a main body configured to receive a medicament cartridge sealed by a penetrable barrier； a cap assembly having an inner needle part and an outer needle part, wherein the inner needle part is movable in a proximal direction with respect to the outer needle part, a needle carrier carrying a needle, the needle carrier being releasably coupled to the inner needle part, wherein, when the inner needle part is displaced in the proximal direction, the inner needle part causes the needle carrier to be displaced axially in the proximal direction； and wherein, subsequent to the axial displacement of the inner needle part, the cap assembly is separable from the main body by movement of the cap assembly in a distal direction.
