Filling device for isobaric filling machines for filling bottles with alimentary liquids, such as in particular sparkling wine and beer, the filling device comprising: a body having an inner cavity which extends vertically through said body; characterized in that: an outer tube, which is fixed at its top to a bottom wall of a tank of the machine intended to contain the liquid with which the bottles are to be filled, extends through the inner cavity of the body and projects downwards relative to the body; an inner tube, which is arranged coaxially with the outer tube, is movable with respect to the outer tube and extends with a lower portion thereof inside the outer tube and projects upwards relative to the outer tube, so as to reach with its top end, in the assembled condition of the filling device on the machine, a level higher than the level of the liquid contained in the tank, the outer tube and the inner tube defining an annular conduit which extends as far as the bottom end of the outer tube and through which the liquid contained in the tank can flow out downwards to fill a bottle; a centring cone which is arranged coaxially with the outer tube and the inner tube and is configured for sealing against the top end of the neck of the bottle to be filled; a first closure member which is arranged so as to be vertically movable and is configured to seal the first annular conduit; a second closure member which is arranged so as to be vertically movable and is configured to seal the inner tube; and an actuation unit configured to control the vertical movement of the first closure member and the second closure member; wherein the first closure member is arranged close to the bottom end of the inner tube and cooperates with the bottom end of the outer tube so as to open/close the annular conduit at the bottom. a body having an inner cavity which extends vertically through said body; characterized in that: an outer tube, which is fixed at its top to a bottom wall of a tank of the machine intended to contain the liquid with which the bottles are to be filled, extends through the inner cavity of the body and projects downwards relative to the body; an inner tube, which is arranged coaxially with the outer tube, is movable with respect to the outer tube and extends with a lower portion thereof inside the outer tube and projects upwards relative to the outer tube, so as to reach with its top end, in the assembled condition of the filling device on the machine, a level higher than the level of the liquid contained in the tank, the outer tube and the inner tube defining an annular conduit which extends as far as the bottom end of the outer tube and through which the liquid contained in the tank can flow out downwards to fill a bottle; a centring cone which is arranged coaxially with the outer tube and the inner tube and is configured for sealing against the top end of the neck of the bottle to be filled; a first closure member which is arranged so as to be vertically movable and is configured to seal the first annular conduit; a second closure member which is arranged so as to be vertically movable and is configured to seal the inner tube; and an actuation unit configured to control the vertical movement of the first closure member and the second closure member; wherein the first closure member is arranged close to the bottom end of the inner tube and cooperates with the bottom end of the outer tube so as to open/close the annular conduit at the bottom.