Abstract: A filling head for a machine for automatic filling of bottles to a constant level, particularly in free air, and a filling machine equipped with such filling heads. The filling head has a circulation chamber into which the filling liquid enters via a feed orifice and from which the filling liquid leaves via a lower outlet orifice which is extended by a discharge tube for penetrating inside a neck of a bottle during filling. A membrane with a projection opens or closes the outlet orifice in response to control signals emitted by a detector of the filling level arranged on a zone of the discharge tube situated inside the bottle during filling.