A medicament delivery device comprising: a housing having a longitudinal axis extending between, and along, a proximal end portion and a distal end portion of the housing, a container holder arranged in the housing at the proximal end portion, an axially movable plunger adapted to be displaced along the longitudinal axis into the container holder, and an energy accumulating member arranged inside the housing, the energy accumulating member being adapted for displacing the plunger along the longitudinal axis towards the proximal end portion, characterized in that the container holder is adapted to accommodate a medicament container adapted for attachment of a medicament delivery member at one end portion of the medicament container and comprising a first piston sealingly and slidably arranged inside an opposite end portion of the medicament container, and a second piston slidably arranged inside an intermediate portion of the medicament container, wherein the plunger comprises an outer plunger rod and an inner plunger rod arranged at least partially inside the outer plunger rod, the inner plunger rod being arranged in threaded engagement with the outer plunger rod, an actuation rod extending at least partially inside the inner plunger rod, wherein the actuation rod is arranged in sliding engagement with the inner plunger rod, that the actuation rod comprises a knob arranged outside the housing at the distal end portion such that upon manual rotation of the knob, the inner plunger rod is rotated and displaced along the longitudinal axis in a direction towards the proximal end portion into the container holder for performing a mixing in the medicament container. a housing having a longitudinal axis extending between, and along, a proximal end portion and a distal end portion of the housing, a container holder arranged in the housing at the proximal end portion, an axially movable plunger adapted to be displaced along the longitudinal axis into the container holder, and an energy accumulating member arranged inside the housing, the energy accumulating member being adapted for displacing the plunger along the longitudinal axis towards the proximal end portion, characterized in that the container holder is adapted to accommodate a medicament container adapted for attachment of a medicament delivery member at one end portion of the medicament container and comprising a first piston sealingly and slidably arranged inside an opposite end portion of the medicament container, and a second piston slidably arranged inside an intermediate portion of the medicament container, wherein the plunger comprises an outer plunger rod and an inner plunger rod arranged at least partially inside the outer plunger rod, the inner plunger rod being arranged in threaded engagement with the outer plunger rod, an actuation rod extending at least partially inside the inner plunger rod, wherein the actuation rod is arranged in sliding engagement with the inner plunger rod, that the actuation rod comprises a knob arranged outside the housing at the distal end portion such that upon manual rotation of the knob, the inner plunger rod is rotated and displaced along the longitudinal axis in a direction towards the proximal end portion into the container holder for performing a mixing in the medicament container.