A foaming device for the preparation of coffee and milk, cappuccinos or similar drinks including a cover designed to close the top of a virtually cylindrical container of the drink and a disk movable axially inside the container during use of the device with the disk being equipped with at least one mesh portion for emulsion of the air in the liquid and being fastened transversely to a rod running axially in a hole in the cover and protruding above it to be grasped manually. The device is characterized in that said cover includes at least two concentric annular grooves designed to engage with the upper edge of containers of different diameters to realize closing of the container with there being present a flexible circumferential portion that extends from the edge of the disk towards the outside to cover the opening that is created between the disk edge and the internal wall of the container when the device is used with containers of greater diameter.