The invention relates to an auto-injector for administering a dose of a liquid medicament (M), comprising of an elongate housing arranged to contain a syringe with a hollow needle and a bung for sealing the syringe and displacing the medicament (M), the elongate housing having a distal end (D) and a proximal end (P) with an orifice intended to be applied against an injection site, wherein the syringe is slidably arranged with respect to the housing; spring means 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 (P) as well as operating the syringe to supply the dose of medicament (M); and activating means arranged to lock the spring means in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring means for injection. The spring means is a torsion spring grounded at one end in the housing and at the other end in a 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, the second gear member prevented from rotating and coupled to the bung in order to push it towards the proximal end (P), 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. The activating means is a trigger button, arranged at a distal end (D) of the housing and operable by being pressed in proximal direction (P).