The wiper has a squeezing pressure head extending crossways to the longitudinal direction and a press strip movable relatively to it, which with the pressure head forms a press gap for the wiping sheet. The pressure head (7) is connected with a guide bush (4) displaceable along the rod (1) and forms a support for the wiping sheet holder connected with the rod. The press strip (16) is connected with a grip sleeve (12) limitedly longitudinally movable relative to the guide bush. Between the guide bush and the grip sleeve a pressure spring (20) is arranged acting in the apparatus longitudinal direction.
