The present invention relates to a medicament delivery device comprising a housing (10, 12)； a medicament delivery member 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 medicament delivery member assembly (62, 66)； an activation mechanism (14) configured to interact with said penetration and withdrawal mechanism (48, 74, 78, 86) for initiating the movement of the medicament delivery member 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 medicament delivery member assembly (62, 66) from the penetration position back to the initial position. The invention is characterized in that penetration and withdrawal mechanism (48, 74, 78, 86) comprises a driver (48) operably connected to said medicament delivery member assembly (62, 66) and to said activation and stop mechanisms (16, 34； 108, 110)； a drive element (74) operably connected to said driver； a biased force element (86) connected to said drive element (74)； a switching element (76) arranged between the driver (48) and the drive element (74)；wherein operation of said activation mechanism (14) allows said biased force element (86) to interact with said drive element (74), causing a movement of said switching element (76) such that said driver (48) is moved towards a predetermined direction and slaves the medicament delivery member assembly (62, 66) to said penetration position； and wherein operation of said stop mechanism (108, 10) allows said biased force element (86) to further interact with said drive element (74), causing movement of said switching element (76) such that said driver (48) is moved in an o
