A compactly constructed locking device with a displaceable securing element fixing a detent element and actuated in a simple way into a detaining position or into a releasing position. The distance between a control cam and the securing element is selected in such a way that, with the detent element in the unlocking position, the control cam is axially displaced with respect to the control contour and is therefore located outside the range of action of the control contour. Only when the electromechanical drive is activated in order to displace the detent element into its locking position does the drive part with the control contour come into engagement with the control cam. The arrangement allows for sudden displacement into the locking position.