Medicament delivery device comprising a housing, which housing is arranged to accommodate a medicament container, further comprising a power pack arranged to exert a force on said medicament container for expelling a dose of medicament, said power pack comprising - a plunger rod; - a drive spring arranged to exert a force on said plunger rod; - an actuator coaxial with said plunger rod and arranged with holding elements for releasibly holding said plunger rod with said drive spring in an energized state; - an actuator sleeve coaxial with said actuator and arranged to interact with said holding elements, said actuator sleeve being movable in a longitudinal direction in relation to the actuator; - a medicament delivery member guard protruding from the proximal end of said housing and movable in said longitudinal direction, said medicament delivery member guard being connected to said actuator sleeve; - a manually operable activator arranged at a distal end of the housing movable in said longitudinal direction and operably connected to said actuator for releasing said plunger rod, characterised in a locking arrangement for releasibly locking said actuator to said actuator sleeve, such that movement of said medicament delivery member guard in a distal direction when pressing the medicament delivery device against an injection site causes said actuator sleeve, said actuator and said plunger rod to move in a distal direction, and that subsequent manual movement of said activator causes a movement of said plunger rod and said actuator in relation to said actuator sleeve in a proximal direction, causing a release of said plunger rod by said actuator; wherein said locking arrangement comprises a flexible member on said actuator provided with a proximally directed stop surface, on which stop surface a distally directed surface of said actuator sleeve will act during movement in said distal direction, preventing relative movement of said actuator in relation to said actuator sleeve in a proximal direction, and that said activator is arranged with ledges acting on said flexible member, removing the contact between the stop surface and the surface of the actuator sleeve, enabling movement of said actuator and said plunger rod. - a plunger rod; - a drive spring arranged to exert a force on said plunger rod; - an actuator coaxial with said plunger rod and arranged with holding elements for releasibly holding said plunger rod with said drive spring in an energized state; - an actuator sleeve coaxial with said actuator and arranged to interact with said holding elements, said actuator sleeve being movable in a longitudinal direction in relation to the actuator; - a medicament delivery member guard protruding from the proximal end of said housing and movable in said longitudinal direction, said medicament delivery member guard being connected to said actuator sleeve; - a manually operable activator arranged at a distal end of the housing movable in said longitudinal direction and operably connected to said actuator for releasing said plunger rod, characterised in a locking arrangement for releasibly locking said actuator to said actuator sleeve, such that movement of said medicament delivery member guard in a distal direction when pressing the medicament delivery device against an injection site causes said actuator sleeve, said actuator and said plunger rod to move in a distal direction, and that subsequent manual movement of said activator causes a movement of said plunger rod and said actuator in relation to said actuator sleeve in a proximal direction, causing a release of said plunger rod by said actuator; wherein said locking arrangement comprises a flexible member on said actuator provided with a proximally directed stop surface, on which stop surface a distally directed surface of said actuator sleeve will act during movement in said distal direction, preventing relative movement of said actuator in relation to said actuator sleeve in a proximal direction, and that said activator is arranged with ledges acting on said flexible member, removing the contact between the stop surface and the surface of the actuator sleeve, enabling movement of said actuator and said plunger rod.