A filling device (10) includes a tubular body (12) including, in an upper section (14), a feeding chamber (18), and provided with a nozzle (20) for the flow of the liquid, wherein a liquid feeding conduit (22) leads into the feeding chamber (18) through a feeding orifice (24), and including a plug (26) which is controlled in axial sliding inside the tubular body (12), between an open position and a closed position. The device includes a servo valve (42, 142) coaxial to the plug (26) which is arranged in the upper section (14) of the tubular body (12). The servo valve (42, 142) includes a wall (44, 144) which partly closes the feeding orifice (24), and the servo valve (42, 142) is pivotingly controlled about its axis (A1) so as to regulate the feeding flow rate by modifying the closure area of the wall (44, 144).