An auto-injector comprising an elongate housing containing a syringe. The housing having a an orifice intended to be applied against an injection site. The syringe is slidably arranged with respect to the housing. A spring pushing the needle from a covered position into an advanced position, operating the syringe and covering the needle. An activator arranged to lock the spring prior to manual operation and capable of, upon manual operation, releasing the spring means for injection. A first gear arrangement and a second gear arrangement arranged for converting torque from a first end and a second end of the torsion spring into a translative force. The first end groundable in the housing while the second end acts on a plunger through the second gear arrangement for advancing the needle and supplying the dose.