A lockable electromechanical actuator (1, 101, 201, 301, 401, 501, 601, 701) comprising: - a body (8, 108, 208, 308, 408, 508, 608); - a motor having its outlet shaft constrained to rotate with a screw (15, 115, 215, 315, 415, 515, 615, 715) extending along a longitudinal axis (Oy); - a nut (19, 719) engaged on the screw (15, 115, 215, 315, 415, 515, 615, 715) and provided with connection means for connection to an element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved, the nut moving on the screw (15, 115, 215, 315, 415, 515, 615, 715) from a retracted first position of the nut (19, 719) to a deployed second position of the nut (19, 719) corresponding respectively to a retracted first position of the element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved and to a deployed second position of the element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved; and - a locking device (40, 140, 240, 340, 440, 540, 640, 1050) for locking the element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved in the retracted position; the locking device (40, 140, 240, 340, 440, 540, 640, 1050) comprising one of the means for actuating a lock (60, 160, 260, 360, 460, 560, 660, 760) being capable of selectively adopting a first position in which the lock (60, 160, 260, 360, 460, 560, 660, 760) prevents relative turning between the screw (15, 115, 215, 315, 415, 515, 615, 715) and the nut (19, 719) that would lead to the element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved being deployed and a second position in which relative rotation between the screw (15, 115, 215, 315, 415, 515, 615, 715) and the nut (19, 719) is free; characterized in that the locking device (40, 140, 240, 340, 440, 540, 640, 1050) is a passive device and is arranged so that: - when the lock (60, 160, 260, 360, 460, 560, 660, 760) is in its first position, the lock (60, 160, 260, 360, 460, 560, 660, 760) passes from the first position to the second position when the element (2, 102, 202, 302, 402, 502, 602) that is to be moved is taken beyond its retracted position; and - when the lock (60, 160, 260, 360, 460, 560, 660, 760) is in its second position, the lock (60, 160, 260, 360, 460, 560, 660, 760) passes from the second position to the first position when the element (2, 102, 202, 302, 402, 502, 602) that is to be moved is taken beyond its retracted position. - a body (8, 108, 208, 308, 408, 508, 608); - a motor having its outlet shaft constrained to rotate with a screw (15, 115, 215, 315, 415, 515, 615, 715) extending along a longitudinal axis (Oy); - a nut (19, 719) engaged on the screw (15, 115, 215, 315, 415, 515, 615, 715) and provided with connection means for connection to an element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved, the nut moving on the screw (15, 115, 215, 315, 415, 515, 615, 715) from a retracted first position of the nut (19, 719) to a deployed second position of the nut (19, 719) corresponding respectively to a retracted first position of the element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved and to a deployed second position of the element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved; and - a locking device (40, 140, 240, 340, 440, 540, 640, 1050) for locking the element (2, 102, 202, 302, 402, 502, 602, 702) that is to be moved in the retracted position; - when the lock (60, 160, 260, 360, 460, 560, 660, 760) is in its first position, the lock (60, 160, 260, 360, 460, 560, 660, 760) passes from the first position to the second position when the element (2, 102, 202, 302, 402, 502, 602) that is to be moved is taken beyond its retracted position; and - when the lock (60, 160, 260, 360, 460, 560, 660, 760) is in its second position, the lock (60, 160, 260, 360, 460, 560, 660, 760) passes from the second position to the first position when the element (2, 102, 202, 302, 402, 502, 602) that is to be moved is taken beyond its retracted position.