Abstract: A locking device prevents simultaneous displacement of two slides in a common plane, each slide being associated with a respective push button. Each slide is returned by a respective spring, and has a ramp and a notch directed towards a bolt placed between the slides and capable, by actuation of a push button, of moving to a working position to prevent movement of the other push button. The improvement is that the bolt is kept at a central rest position, equidistant from the ramps, by a resilient element. When the bolt is placed in working position by actuation of a first push button, actuation of the second push button causes the bolt to be kept in that position. In the working position, there is complete absence of any contact, between the bolt and the first slide, which might otherwise prevent the return movement of the first slide.