An actuation mechanism to be used with a medicament delivery device, comprising a generally tubular distal housing part and a generally tubular proximal housing part the actuation mechanism comprising: - a plunger rod arranged to act on a stopper of a medicament container; - an actuator arranged slidable and connected to the plunger rod for acting on the stopper when said actuator is operated by displacing it in a longitudinal direction of the actuation mechanism; - an activator comprising a generally tubular activator sleeve provided with a spirally extending groove on its outer surface, the activator sleeve is arranged rotational and slidable in the longitudinal direction inside the distal the housing part, wherein said activator sleeve comprises protrusions arranged to interact with said actuator such that said activator sleeve is rotated when said actuator is operated, wherein said actuator is arranged with ledges cooperating with said protrusions, which ledges are arranged inclined in relation to the longitudinal direction; wherein said actuator is arranged with locking elements (92, 94) arranged to cooperate with said protrusions of said activator sleeve such as to lock said actuator after operation for delivering a dose of medicament; - said groove arranged with a length corresponding to the total amount of medicament to be delivered in a number of doses contained in said medicament container, - said groove provided with an end wall, - a stop ring arranged coaxial with said activator sleeve; - said activator sleeve and the stop ring are arranged such that a follower of the stop ring is arranged on an inner surface of the stop ring and positioned in said groove, said follower is arranged to abut said end wall at the proximal end of the activator sleeve of said groove when said total amount has been delivered. - a plunger rod arranged to act on a stopper of a medicament container; - an actuator arranged slidable and connected to the plunger rod for acting on the stopper when said actuator is operated by displacing it in a longitudinal direction of the actuation mechanism; - an activator comprising a generally tubular activator sleeve provided with a spirally extending groove on its outer surface, the activator sleeve is arranged rotational and slidable in the longitudinal direction inside the distal the housing part, wherein said activator sleeve comprises protrusions arranged to interact with said actuator such that said activator sleeve is rotated when said actuator is operated, wherein said actuator is arranged with ledges cooperating with said protrusions, which ledges are arranged inclined in relation to the longitudinal direction; wherein said actuator is arranged with locking elements (92, 94) arranged to cooperate with said protrusions of said activator sleeve such as to lock said actuator after operation for delivering a dose of medicament; - said groove arranged with a length corresponding to the total amount of medicament to be delivered in a number of doses contained in said medicament container, - said groove provided with an end wall, - a stop ring arranged coaxial with said activator sleeve; - said activator sleeve and the stop ring are arranged such that a follower of the stop ring is arranged on an inner surface of the stop ring and positioned in said groove, said follower is arranged to abut said end wall at the proximal end of the activator sleeve of said groove when said total amount has been delivered.