The present invention relates to a medicament delivery device comprising a distal housing part (10) a proximal housing part (12), said proximal housing part being arranged to accommodate a multi-compartment medicament container (34), wherein said housing parts are designed and arranged to be movable in relation to each other from a first position in which said housing parts are partially extended in relation to each other, to a second position in which said housing parts are partially retracted in relation to each other a drive mechanism arranged in said distal housing part (10) comprising a plunger rod (44) and an auto mixing mechanism configured to hold said housing parts in the first position and to lock said housing parts in the second position wherein said auto mixing mechanism comprises a mixing force member (30) operably arranged between said housing parts, such that manual activation of said auto mixing mechanism allows said mixing force member (30) to cause the two housing parts to move from the first position to the second position whereby said plunger rod (44) acts on said multi-chamber medicament container (34) to perform a mixing of a medicament contained in said multi-compartment medicament container (34).
