The present disclosure relates to an administration mechanism (9) for a medicament delivery device (1), comprising: a linearly displaceable medicament delivery member cover (7), an actuator sleeve (11), an actuator (13) configured to be received by the actuator sleeve (11), wherein the medicament delivery member cover (7) is configured to axially displace the actuator sleeve (11) from an initial position to a distally displaced position thereby displacing the actuator sleeve (11) relative to the actuator (13), a rotator (25) having a guide structure and configured to be received by the actuator (13), a plunger holder (21) configured to be received by and engage with the rotator (25), which rotator (25) and plunger holder (21) are configured to be proximally biased, and a plunger rod (23) configured to be received by and engage with the plunger holder (21) in the initial position of the actuator sleeve (11), which plunger rod (23) is configured to be proximally biased, wherein the actuator (13) is configured to engage with the plunger holder (21) in the initial position of the actuator sleeve (11), thereby preventing the plunger holder (21) from proximal displacement relative to the actuator (13), wherein the actuator (13) is configured to be released from engagement with the plunger holder (21) by displacement of the actuator sleeve (11) towards the distally displaced position, thereby enabling proximal displacement of the plunger holder (21), the plunger rod (23) and the rotator (25) relative to the actuator (13), whereby the actuator (13) is configured to engage with the guide structure of the rotator (25) and to rotate the rotator (25) relative to the plunger holder (21), releasing the plunger rod (23) from the plunger holder (21).
