A drive unit for a medicament delivery device is presented having an elongated plunger rod extending in a longitudinal direction, a drive force element capable of applying a drive force on the elongated plunger rod, and an actuator operably connected to the elongated plunger rod for releasably holding the elongated plunger rod in an energized state when the drive force element is exerting a drive force on the elongated plunger rod. An activator is operably connected to the actuator for releasably holding the actuator in a holding position where the actuator is designed to be movable from the holding position in a direction generally transversal to the longitudinal direction upon a displacement of the activator for releasing the plunger rod.