The present invention relates to medicament delivery device comprising a generally tubular distal housing part (19) a generally tubular medicament container holder (16) a medicament container (18) a plunger rod (32) resilient force an actuation means (34) comprising flexible locking means and an activation button a release means (40) and a resilient means (60) characterised in that said plunger rod comprises a number of stop engagements (38) arranged on its outer circumferential surface and arranged to co-act with corresponding stop engagements (37) on the flexible locking means, such that when said activation button is proximally depressed said stop engagement (37) on said flexible locking means come out of contact from one stop engagement (38) of the plunger rod and such that when said activation button (48) is released, said resilient means (60) forces the activation button and thereby the flexible locking means to move distally such that said stop engagements (37) on said flexible locking means come into contact with another stop engagement (38) of the plunger rod.
