A connecting device includes a plug connector receivable into a receiving space of a mating connector. In a connection position, a latching arm of the plug connector is engaged with a latch receiver of the mating connector. The plug connector has a securing unit for locking and releasing the latching arm. The mating connector has a counterstop element which, when the plug connector is introduced into the receiving space, strikes a deflection chamfer of the securing unit and deflects a securing arm of the securing unit perpendicularly to the direction of insertion and in parallel to a base side of the plug connector so that, in the connection position, a stop surface of the securing unit is arranged at an offset from a stopper element of the securing unit, and the securing unit is movable into a locked position.