A drug delivery device comprising or adapted to receive a drug-filled cartridge, comprising: - a housing (50, 470), - a piston rod adapted to engage and axially displace a piston in a loaded cartridge in a distal direction to thereby expel a dose of drug from the cartridge, - a transmission member (210, 211) defining an axis, - a drive spring coupled to the transmission member, - a drive member (420, 421) in engagement with the piston rod and adapted to be rotated by the transmission member to thereby move the piston rod distally during expelling, - dose setting means (110, 160) allowing a user to simultaneously set a dose amount to be expelled and strain the drive spring correspondingly by rotation of the transmission member, the dose setting means comprising a dose setting member which during dose setting is rotationally coupled to the transmission member and adapted to rotate in a first direction to set a dose, - a releasable ratchet mechanism (162, 222, 168, 179) allowing the dose setting member to be rotated in the first direction to a set rotational position, - a releasable clutch mechanism (250, 440, 470) adapted to rotationally lock the drive member relative to the housing during dose setting, - release means (161, 191, 254, 444) actuatable between a dose setting mode and an expelling mode, characterized in that the clutch mechanism comprises: - a relative to the housing axially non-moveable clutch member, and - a relative to the housing rotationally non-moveable locking member, wherein during dose setting and dose expelling the clutch member is rotationally locked to the drive member (420, 421), wherein the transmission member (210, 211) is actuatable between a dose setting state in which it is allowed to rotate relative to the clutch member, and an expelling state in which it is rotationally coupled to the clutch member, wherein the locking member is actuatable between a dose setting state in which it is in rotationally locked engagement (254, 444) with the clutch member, and an expelling state in which it is rotationally decoupled from the clutch member, wherein, when the release means is actuated from the dose setting mode to the expelling mode: - the transmission member (210, 211) is actuated from its dose setting state to its expelling state, - the locking member is actuated from its dose setting state to its expelling state, and - the ratchet mechanism is released, whereby the strained drive spring is allowed to rotate the transmission member and the drive member and thereby move the piston rod distally. - a housing (50, 470), - a piston rod adapted to engage and axially displace a piston in a loaded cartridge in a distal direction to thereby expel a dose of drug from the cartridge, - a transmission member (210, 211) defining an axis, - a drive spring coupled to the transmission member, - a drive member (420, 421) in engagement with the piston rod and adapted to be rotated by the transmission member to thereby move the piston rod distally during expelling, - dose setting means (110, 160) allowing a user to simultaneously set a dose amount to be expelled and strain the drive spring correspondingly by rotation of the transmission member, the dose setting means comprising a dose setting member which during dose setting is rotationally coupled to the transmission member and adapted to rotate in a first direction to set a dose, - a releasable ratchet mechanism (162, 222, 168, 179) allowing the dose setting member to be rotated in the first direction to a set rotational position, - a releasable clutch mechanism (250, 440, 470) adapted to rotationally lock the drive member relative to the housing during dose setting, - release means (161, 191, 254, 444) actuatable between a dose setting mode and an expelling mode, characterized in that - a relative to the housing axially non-moveable clutch member, and - a relative to the housing rotationally non-moveable locking member, - the transmission member (210, 211) is actuated from its dose setting state to its expelling state, - the locking member is actuated from its dose setting state to its expelling state, and - the ratchet mechanism is released,