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.
