Abstract: An apparatus for actuating the rod of a presser element of a mixing machine of the internal type which has a lower mixing assembly and an upper structure for feeding of the material. At least one pair of guides are arranged opposite each other on the sides of the feed structure parallel to the longitudinal axes of the machine and in a symmetrical position with respect to the latter on the opposite sides of a transverse horizontal axis. At least one pair of cylinders are fixed to the guides and having their rods of their pistons connected to a cross-member travelling via wheels on the guides. The top end of the presser rod is hinged to the cross member. The rod also slides while being guided by a sealing group integral in the axial direction with the cover of the feed hopper and movable with respect to the latter in a horizontal plane so as to allow the oscillating movement of the rod with respect to the longitudinal axis of the machine.