An injection device, comprising: - a housing including a container carrier having a medicament container and a needle attached to the medicament container; - a needle shield slidable arranged inside said housing with a contact part intended to be applied against an injection site; - activation means arranged to be interactively connected to said needle shield and capable of, upon manual activation, initiating a penetration sequence, wherein the activation means comprises flexible arms having inwardly extending ledges on a penetration sleeve, recesses on a lock-out sleeve, a circumferential groove on an activation housing, and an activation button having inwardly extending parts facing the arms; - penetration means interactively connected to said activation means and capable of performing an automatic penetration of the needle, wherein the penetration means comprises tongues arranged on an activation housing and snap-fitted to the container carrier, outwardly extending protrusions arranged on flexible arms which are arranged on said activation housing; a retraction release ring abutting said outwardly extending protrusions, and a penetration spring arranged between the retraction release ring and an inner rear wall of the penetration sleeve; - injection means interactively connected to said penetration means and capable of triggering and performing an automatic injection of the medicament, wherein the injection means comprises flexible tongues arranged on an activation housing and where each tongue is arranged with inwardly directed ledges; a plunger rod having a circumferential groove where the ledges are positioned by an injection release ring when the device is unarmed; and an injection spring arranged between a front wall of the plunger rod and a rear wall of the activation housing; - withdrawing means interactively connected to said injection means and capable of triggering and performing an automatic withdrawing of the needle, wherein the withdrawing means comprises a penetration retraction spring arranged between the retraction release ring and protrusions arranged on an activation housing; and the flexible arms arranged on said activation housing; characterized in that said device further comprises an active triggering withdrawal mechanism interactively connected to said withdrawing means and capable of allowing said with drawing means to be triggered when the injection device starts to be removed from the injection site, wherein the active triggering withdrawal mechanism comprises grooves arranged on a lock plate surrounding the activation housing, and corresponding ledges arranged on the protrusions of the flexible arms such that when the penetration spring urges the activation housing and the container carrier forward, the ledges come into engagement with the grooves for preventing the flexible arms from being moved inwards; and when the injector is removed or lifted from the injection site, a front surface of the lock-out sleeve causes the lock plate to move forward such that the ledges come out of contact with the grooves, enabling the flexible arms to collapsing inwards allowing the retraction release ring to pass the protrusions of the flexible arms such that the container carrier is drawn into the housing of the injector by the force of the retraction spring acting on the protrusions. - a housing including a container carrier having a medicament container and a needle attached to the medicament container; - a needle shield slidable arranged inside said housing with a contact part intended to be applied against an injection site; - activation means arranged to be interactively connected to said needle shield and capable of, upon manual activation, initiating a penetration sequence, wherein the activation means comprises flexible arms having inwardly extending ledges on a penetration sleeve, recesses on a lock-out sleeve, a circumferential groove on an activation housing, and an activation button having inwardly extending parts facing the arms; - penetration means interactively connected to said activation means and capable of performing an automatic penetration of the needle, wherein the penetration means comprises tongues arranged on an activation housing and snap-fitted to the container carrier, outwardly extending protrusions arranged on flexible arms which are arranged on said activation housing; a retraction release ring abutting said outwardly extending protrusions, and a penetration spring arranged between the retraction release ring and an inner rear wall of the penetration sleeve; - injection means interactively connected to said penetration means and capable of triggering and performing an automatic injection of the medicament, wherein the injection means comprises flexible tongues arranged on an activation housing and where each tongue is arranged with inwardly directed ledges; a plunger rod having a circumferential groove where the ledges are positioned by an injection release ring when the device is unarmed; and an injection spring arranged between a front wall of the plunger rod and a rear wall of the activation housing; - withdrawing means interactively connected to said injection means and capable of triggering and performing an automatic withdrawing of the needle, wherein the withdrawing means comprises a penetration retraction spring arranged between the retraction release ring and protrusions arranged on an activation housing; and the flexible arms arranged on said activation housing;