The present invention relates to a medicament delivery device comprising a housing which housing is arranged to accommodate a medicament container a drive unit arranged in said housing and capable of acting on a movable stopper positioned inside said medicament container for expelling a dose of medicament wherein said drive unit comprises an elongated plunger rod and a dual back to back force spring assembly operatively connected to said plunger rod such as to provide a symmetrical load on said plunger rod a locking and release mechanism operatively connected to said drive unit and capable of releasing said drive unit upon activation wherein the locking and release mechanism comprises a hold member operatively connected to the plunger rod a rotator member operatively connected to the hold member and a tubular actuation member linearly slidable in relation to the housing and operatively connected to the rotator member where in the hold member is fixedly attached to the housing and comprises a generally tubular lock tube through which the plunger rod extends and two seats designed as half cylinders open towards the proximal direction for housing the dual back to back force spring assembly and wherein the lock tube comprises resilient locking and release means configured to interact with both the plunger rod and the rotator member.
