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 comprising an inner circumferential surface having inner ledges and inner grooves , the rotator member being 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; characterised in that 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 that are two oppositely positioned radial flexible tongues , each with a first radial inwardly directed protrusion and with a first radial outwardly directed protrusion ; wherein the rotator member is arranged to be rotated from a locked position to a released position; wherein the first radial outwardly directed protrusion and the ledge forces the radial flexible tongues radial inwards such that the first radial inwardly directed protrusions are engaged into recesses of the plunger rod in the locked position; and the first radial outwardly directed protrusions and the inner groove forces the radial flexible tongues radial outwards such that the first radial inwardly directed protrusions are disengaged from the recesses of the plunger rod in the released position for releasing the plunger rod and the spring assembly from the loaded state. - 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 comprising an inner circumferential surface having inner ledges and inner grooves , the rotator member being 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; characterised in that 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 that are two oppositely positioned radial flexible tongues , each with a first radial inwardly directed protrusion and with a first radial outwardly directed protrusion ; <EOS>