Auto-injector for administering a dose of a liquid medicament comprising a clutch mechanism for transmission of a rotary movement from a gear arrangement comprising a first gear member and a second gear member, the first gear member rotatable about a longitudinal axis but axially fixed wherein the first gear member, upon rotation, is arranged for translatively moving a second gear member which is prevented from rotating, wherein the clutch mechanism comprises a circumferential shoulder arranged at the second gear member and at least one resilient clutch finger with a respective inclined inner surface arranged at the first gear member, wherein the clutch mechanism further comprises a tube arranged around the clutch finger, the tube having a number of internal longitudinal splines for engaging the flexed-out clutch finger, the auto-injector further comprising: - an elongate housing arranged to contain a syringe with a hollow needle and a bung for sealing the syringe and displacing the medicament, the elongate housing having a distal end and a proximal end with an orifice intended to be applied against an injection site, - a torsion spring capable of, upon activation, operating the syringe to supply the dose of medicament, wherein the torsion spring is grounded at one end in the housing and at the other end in the first gear member, wherein the second gear member is a piston rod coupled to the bung in order to push it towards the proximal end, - activating means arranged to lock the torsion spring in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the torsion spring for injection, wherein the first gear member is engaged with the activating means prior to manual operation in a manner to prevent rotation and disengaged from the activating means upon manual operation, characterized in that the shoulder is arranged for increasingly pressing against the inclined surface thereby flexing the clutch finger outward when the shoulder reaches the clutch finger in the course of its translation, wherein the syringe is slidably arranged with respect to the housing, - wherein the torsion spring is also capable of, upon activation, pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end, the torsion spring arranged around the tube, the piston rod having an axial bore for slidably arranging the piston rod on a shaft attached to the housing, the axial bore and the shaft having corresponding non-circular profiles, - an outer rear tube coupled with the tube near the distal end of the auto-injector, - a needle shroud biased by a compression spring towards an advanced position and locked in a drawn back position by a locking means, wherein when the clutch fingers are engaged with the internal longitudinal splines the outer rear tube is rotated so as to disengage the bayonet fit by the pin coming clear of the track shoulder so the needle shroud may be pushed forward by the compression spring, wherein the essentially tube-shaped needle shroud is arranged around the syringe in the housing, the needle shroud slideable between at least the drawn back position with the needle shroud almost hidden inside the housing and the advanced position with the needle shroud protruding from the proximal end and covering the hollow needle in its advanced position, wherein the locking means is releasable by rotary movement transmitted by the clutch mechanism which is engaged by the second gear member shortly before the second gear member is fully advanced during an injection stroke. - an elongate housing arranged to contain a syringe with a hollow needle and a bung for sealing the syringe and displacing the medicament, the elongate housing having a distal end and a proximal end with an orifice intended to be applied against an injection site, - a torsion spring capable of, upon activation, operating the syringe to supply the dose of medicament, wherein the torsion spring is grounded at one end in the housing and at the other end in the first gear member, wherein the second gear member is a piston rod coupled to the bung in order to push it towards the proximal end, - activating means arranged to lock the torsion spring in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the torsion spring for injection, wherein the first gear member is engaged with the activating means prior to manual operation in a manner to prevent rotation and disengaged from the activating means upon manual operation, - wherein the torsion spring is also capable of, upon activation, pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end, the torsion spring arranged around the tube, - an outer rear tube coupled with the tube near the distal end of the auto-injector, - a needle shroud biased by a compression spring towards an advanced position and locked in a drawn back position by a locking means,