Filling device for filling an aerosol container with a liquid, such as paint, which device comprises a cup for the liquid for the aerosol container, which cup is provided with an injection opening at its bottom surface; a pusher element for pushing the liquid from the cup via the injection opening to the aerosol container; and a piston head that is adapted to be detachably fixed on the end of the pusher element to be in contact with the liquid in the cup when the liquid is transferred from the cup to the aerosol container, which piston head is in the form of a scrap-er in continuous contact with the side wall of the cup during the liquid transferring operation, wherein the detachable fixing of the piston head allows the piston head to be withdrawn together with the pusher element from the cup after the liquid transferring operation is done.