Abstract: An illumination device for a liquid contained in a container for checking the liquid. The device includes a device for positioning the container and a light source arranged to illuminate the liquid via the base of the container with a light beam aligned along the axis of the container. The invention resides in a mechanism for shaping the light beam issuing from the light source, disposed between the source and the base of the container, and which cooperates with the optical system constituted by the base itself and the liquid, if in contact with the base, in such a fashion that the beam passes substantially through the whole of the volume of the liquid without impinging on the side walls of the container which are in contact with the liquid. The image of the light source the other side of the mechanism for shaping and the container base is preferably located in the neighborhood of the end surface of the liquid, or past it.