A medicament delivery device includes a housing, a container holder in the housing, an axially movable plunger, and an energy accumulating member adapted for displacing the plunger. The container holder is configured to accommodate a medicament container that includes a first piston arranged inside an opposite end portion of the container and a second piston arranged inside an intermediate portion of the container. The plunger includes an outer plunger rod, an inner plunger rod at least partially inside the outer plunger rod, a biassing arrangement for actuating the inner plunger rod, and a locking arrangement that, in a first state, locks the biassing arrangement in an energy-storing position and, in a second state, releases the biassing arrangement from the energy-storing position to displace the inner plunger rod into the container holder.