A lock is fitted with a locking element and a control element which is rotated by a drive to-and-fro in order to axially reciprocate the locking element through a coaxial drive element between a locked and an unlocked position. The drive element and the control element are also configured coaxially and cooperative by means of a cross-pin which is axially displaceable in a transverse borehole of the inner drive element and by means of two helical inner channels as well as an adjoining plane terminal surface of the outer control element which runs perpendicular to the axis of rotation of the control element and is bounded by a side ramp running from the bottom of one channel past the other channel on the outside thereof toward the drive element. The drive element and control element cooperate in such manner that when the control element rotates in that direction in which the cross-pin runs in the channels toward the terminal surface, the drive element shall be commensurately axially displaced and remain in the axial position it has reached until the control element is rotated in the opposite direction and the cross-pin moves in the channels away from the terminal surface causing the drive element to move axially in the opposite direction.