A medicament delivery device has a housing and a sleeve; a shield within and protruding from the housing; a container having a delivery member, a chamber containing a medicament, and a piston; a drive mechanism having a spring and a plunger rod in contact with the piston; and a container holder having a first locking device releasably connected to a corresponding locking device on the sleeve for holding the holder in an initial state against the drive mechanism and a second locking device surrounded by the sleeve and releasably connected to a corresponding locking device on the plunger rod for protecting the piston from force from the drive mechanism until the holder has moved a certain predetermined distance. The shield releases the first locking device when the shield is pressed against a medicament delivery site, whereby the drive mechanism forces the holder the certain predetermined distance.