A medicament delivery device comprising - a housing (10, 16) having at least one housing part (10, 16), that said housing is arranged to receive a medicament container, - a drive unit arranged to act on a stopper in said medicament container, which drive unit comprises a torsion drive spring, - a dose setting member operably connected to said drive unit such that a manual turning of said dose setting member causes a tensioning of said torsion drive spring, - an activation mechanism having an activation button protruding through the distal end of the device, and - said activation mechanism being operably connected to said drive unit such that actuation of said activation mechanism causes a release of said drive unit whereby a set dose of medicament is delivered characterised in that it further comprises - an elongated plunger rod extending in the longitudinal direction of the device provided with threads on its outer surface and having a proximal end arranged to be in contact with said stopper, - a drive nut provided with a central passage arranged with threads cooperating with the threads of said plunger rod, and - that said drive unit comprises a drive member having a proximal end operably engaging said drive nut and drivably connected to said torsion drive spring such that, upon actuation of said activation mechanism, said drive nut as well as said drive member are rotated, whereby said plunger rod is moved in the proximal direction of the device, and wherein said activation mechanism comprises actuation members (84, 92) attached to said activation button and extending in the proximal direction of the device, a drive nut lock member attached to said actuation members (84, 92), which drive nut lock member is releasibly engaging and locking said drive nut via cooperating locking members (80, 82) until said actuation button is moved in the proximal direction, whereby said drive nut is released. - a housing (10, 16) having at least one housing part (10, 16), that said housing is arranged to receive a medicament container, - a drive unit arranged to act on a stopper in said medicament container, which drive unit comprises a torsion drive spring, - a dose setting member operably connected to said drive unit such that a manual turning of said dose setting member causes a tensioning of said torsion drive spring, - an activation mechanism having an activation button protruding through the distal end of the device, and - said activation mechanism being operably connected to said drive unit such that actuation of said activation mechanism causes a release of said drive unit whereby a set dose of medicament is delivered characterised in that it further comprises - an elongated plunger rod extending in the longitudinal direction of the device provided with threads on its outer surface and having a proximal end arranged to be in contact with said stopper, - a drive nut provided with a central passage arranged with threads cooperating with the threads of said plunger rod, and - that said drive unit comprises a drive member having a proximal end operably engaging said drive nut and drivably connected to said torsion drive spring such that, upon actuation of said activation mechanism, said drive nut as well as said drive member are rotated, whereby said plunger rod is moved in the proximal direction of the device, and