A medicament delivery device comprising: - a tubular housing having a proximal end and an opposite distal end; - drive means configured to act on a medicament container for expelling a medicament, wherein the drive means comprises a plunger rod and a first resilient member which is pre-tensioned arranged within the plunger rod; - holding means configured to hold said drive means in a pre-tensioned state; and - activation means configured to interact with said holding means for releasing the drive means from the pre-tensioned state, wherein the activation means is a tubular activation member, characterized in that the holding means are a tubular extension part fixedly connected to the distal end of the tubular housing and a tubular operation member which is interactively connected both to the tubular extension part and to the tubular activation member, wherein the tubular operation member comprises a first co-acting means (101, 102) interactively connected to a corresponding first co-acting means of the tubular activation member and a second co-acting means interactively connected to a corresponding second co-acting means of the tubular extension part; wherein the plunger rod comprises a releasable engaging means interactively connected to the corresponding second co-acting means of the tubular extension part, wherein the plunger rod comprises a proximal end wall being in contact with a slidable stopper, wherein, when said tubular activation member is pressed against a delivery site, the first corresponding co-acting means is configured to be guided within the first co-acting means (101, 102) to force the tubular operation member to rotate, wherein, when the tubular operation member is rotated, the second co-acting means is configured to allow the corresponding second co-acting means to extend in a radial direction, thereby releasing the releasable engaging means and the plunger rod for exerting a pressure on a medicament container and thereby expelling the medicament, and wherein the device further comprises feedback means configured to interact both with said holding means and with said drive means for generating an audible and/or tactile and/or visual signal indicating that the medicament has been completely expelled, wherein said feedback means is a longitudinally extending signal generating member interactively connected to said tubular extension part and to said drive means, such that when the plunger rod is completely released from the tubular extension part and the longitudinally extending signal generating member, the longitudinally extending signal generating member is released from said tubular extension part and displaced distally by a remaining force of the first resilient member for generating an audible and/or tactile and/or visual signal indicating that the medicament has been completely expelled. - a tubular housing having a proximal end and an opposite distal end; - drive means configured to act on a medicament container for expelling a medicament, wherein the drive means comprises a plunger rod and a first resilient member which is pre-tensioned arranged within the plunger rod; - holding means configured to hold said drive means in a pre-tensioned state; and - activation means configured to interact with said holding means for releasing the drive means from the pre-tensioned state, wherein the activation means is a tubular activation member, characterized in that the holding means are a tubular extension part fixedly connected to the distal end of the tubular housing and a tubular operation member which is interactively connected both to the tubular extension part and to the tubular activation member, wherein the tubular operation member comprises a first co-acting means (101, 102) interactively connected to a corresponding first co-acting means of the tubular activation member and a second co-acting means interactively connected to a corresponding second co-acting means of the tubular extension part; wherein the plunger rod comprises a releasable engaging means interactively connected to the corresponding second co-acting means of the tubular extension part, wherein the plunger rod comprises a proximal end wall being in contact with a slidable stopper, wherein, when said tubular activation member is pressed against a delivery site, the first corresponding co-acting means is configured to be guided within the first co-acting means (101, 102) to force the tubular operation member to rotate, wherein, when the tubular operation member is rotated, the second co-acting means is configured to allow the corresponding second co-acting means to extend in a radial direction, thereby releasing the releasable engaging means and the plunger rod for exerting a pressure on a medicament container and thereby expelling the medicament, and wherein the device further comprises feedback means configured to interact both with said holding means and with said drive means for generating an audible and/or tactile and/or visual signal indicating that the medicament has been completely expelled, wherein said feedback means is a longitudinally extending signal generating member interactively connected to said tubular extension part and to said drive means, such that when the plunger rod is completely released from the tubular extension part and the longitudinally extending signal generating member, the longitudinally extending signal generating member is released from said tubular extension part and displaced distally by a remaining force of the first resilient member for generating an audible and/or tactile and/or visual signal indicating that the medicament has been completely expelled.