The present invention relates to a drive mechanism of a drug delivery device for dispensing of a dose of a medicament, comprising:- a housing (22, 24) of substantially cylindrical geometry having a long axis extending in an axial direction,- an at least axially displaceable piston rod (12) adapted to become operably engaged with a piston of a cartridge containing the medicament for displacing the piston in a distal direction,- at least one actuation means (18, 19) radially displaceable with respect to the housing (22, 24) by an externally applied depressing force for transferring a respective driving force to the piston rod (12), and- a coupling means operably engaged with the actuation means (18, 19) and with the piston rod (12) adapted to transfer the radially inwardly directed displacement of the at least one actuation means (18, 19) into a distally directed axial displacement of the piston rod (12).
