A medicament delivery device includes a distal housing part a proximal housing part in which a multi-chamber medicament container is arranged, with the proximal housing part movable relative to the distal housing part for mixing substances in the container a plunger rod arranged to act on a stopper in the container, where movement of the housing parts toward each other forces the stopper against the plunger rod for mixing the substances in the container a drive force unit for forcing the plunger rod for subsequent delivery of medicament an activation member slidable through the distal housing part and releasably connected to the drive force unit and a guide shell one-way rotatable in the distal housing part with threads that cooperate with threads on the proximal housing part. The guide shell and plunger rod have guide members such that they are rotationally locked but slidable in relation to each other.
