Medicament delivery device comprising - a housing (10, 12); - an injection needle assembly (62, 66) configured to be moved in relation to the housing (10, 12) from an initial position to a penetration position and from the penetration position back to the initial position; - a penetration and withdrawal mechanism (48, 74, 78, 86) configured to control the movements of said injection needle assembly (62, 66); - an activation mechanism configured to interact with said penetration and withdrawal mechanism (48, 74, 78, 86) for initiating the movement of the injection needle assembly (62, 66) from the initial position to the penetration position; - a stop mechanism (108, 110) configured to interact with said penetration and withdrawal mechanism (48, 74, 78, 86) for initiating the movement of the injection needle assembly (62, 66) from the penetration position back to the initial position; characterized in that penetration and withdrawal mechanism (48, 74, 78, 86) comprises: - a driver comprising a rotator sleeve operably connected to said injection needle assembly (62, 66) and to a drive element, said drive element comprising a flexible, non-elastic, band wound around said rotator sleeve; - a biased force element connected to said drive element; - a switching element arranged between the rotator sleeve and the band, which switching element is releasibly attached to said rotator sleeve and arranged to alter the winding direction of said band around said rotator sleeve; wherein the rotation of said rotator sleeve will cause a linear movement of said injection needle assembly (62, 66); wherein operation of said activation mechanism allows said biased force element to pull said band, causing a rotation of said rotator sleeve in one direction and slaves the injection needle assembly (62, 66) to said penetration position; and wherein operation of said stop mechanism (108, 110) releases said switching element so that the altered winding direction causes said rotator sleeve to be rotated in an opposite direction and slaves said injection needle assembly (62, 66) back to said initial position. - a housing (10, 12); - an injection needle assembly (62, 66) configured to be moved in relation to the housing (10, 12) from an initial position to a penetration position and from the penetration position back to the initial position; - a penetration and withdrawal mechanism (48, 74, 78, 86) configured to control the movements of said injection needle assembly (62, 66); - an activation mechanism configured to interact with said penetration and withdrawal mechanism (48, 74, 78, 86) for initiating the movement of the injection needle assembly (62, 66) from the initial position to the penetration position; - a stop mechanism (108, 110) configured to interact with said penetration and withdrawal mechanism (48, 74, 78, 86) for initiating the movement of the injection needle assembly (62, 66) from the penetration position back to the initial position; - a driver comprising a rotator sleeve operably connected to said injection needle assembly (62, 66) and to a drive element, said drive element comprising a flexible, non-elastic, band wound around said rotator sleeve; - a biased force element connected to said drive element; - a switching element arranged between the rotator sleeve and the band, which switching element is releasibly attached to said rotator sleeve and arranged to alter the winding direction of said band around said rotator sleeve;