A drive mechanism of a drug delivery device for dispensing of a dose of a medicament, the mechanism comprising: - an elongated housing extending in an axial direction (1, 2), - a piston rod to operably engage with a piston of a cartridge to displace the piston in axial distal direction, - a drive sleeve rotatably supported in the housing at least in a dose incrementing direction against the action of a spring element for setting of a dose, and wherein during a dose dispensing procedure: a) the drive sleeve is driven by the relaxing spring element in an opposite dose decrementing direction and b) the drive sleeve is operably connected with the piston rod for driving the piston rod in the axial distal direction, - a ratchet mechanism to rotatably fix the drive sleeve relative to the housing, the ratchet mechanism comprises a first ratchet body and a second ratchet body,, - wherein one of the first and second ratchet bodies (151; 152) is operably engaged with the housing and wherein the other one of the first and second ratchet bodies (152, 151) is operably engaged with the drive sleeve, characterized in that - the first ratchet body has a first and a second ratchet element (94, 95) to alternately engage with a toothed profile of the second ratchet body, wherein the position and geometrical shape of the ratchet elements (94, 95) is such that one of the ratchet elements is engaged with the toothed profile while the other one of the ratchet elements is disengaged from the toothed profile and vice versa and wherein the first ratchet element is phase shifted to the second ratchet element with regard to the period of the toothed profile of the second ratchet body. - an elongated housing extending in an axial direction (1, 2), - a piston rod to operably engage with a piston of a cartridge to displace the piston in axial distal direction, - a drive sleeve rotatably supported in the housing at least in a dose incrementing direction against the action of a spring element for setting of a dose, and wherein during a dose dispensing procedure: a) the drive sleeve is driven by the relaxing spring element in an opposite dose decrementing direction and b) the drive sleeve is operably connected with the piston rod for driving the piston rod in the axial distal direction, a) the drive sleeve is driven by the relaxing spring element in an opposite dose decrementing direction and b) the drive sleeve is operably connected with the piston rod for driving the piston rod in the axial distal direction, - a ratchet mechanism to rotatably fix the drive sleeve relative to the housing, the ratchet mechanism comprises a first ratchet body and a second ratchet body,, - wherein one of the first and second ratchet bodies (151; 152) is operably engaged with the housing and wherein the other one of the first and second ratchet bodies (152, 151) is operably engaged with the drive sleeve, characterized in that - the first ratchet body has a first and a second ratchet element (94, 95) to alternately engage with a toothed profile of the second ratchet body, wherein the position and geometrical shape of the ratchet elements (94, 95) is such that one of the ratchet elements is engaged with the toothed profile while the other one of the ratchet elements is disengaged from the toothed profile and vice versa and wherein the first ratchet element is phase shifted to the second ratchet element with regard to the period of the toothed profile of the second ratchet body.