The present invention relates to an injection device for automatic torsion spring driven injection of a liquid drug. The injection device is of the type wherein a telescopically movable needle shield (20) activates the release of the torque of the torsion spring to drive the injection when the needle shield is moved from its extended position to a retracted position. The injection device is provided with a needle interface (30) carrying the injection needle, which needle interface is provided with means (32) preventing axial movement of the shield when no injection needle is mounted. Further, other means are provided to restrain the needle shield in the retracted position when the injection device is its “zero” position such that a user has access to the injection needle in order to exchange the injection needle.
