A packaging and filling machine is capable of easily preforming with the forming flaps by keeping the pressure of the filled liquid food in the tube the positive pressure, capable of preventing the pressure of the liquid food from dropping to negative pressure, even if the pressure of the liquid food decreases due to the up-and-down of the liquid food pressure, and capable of preventing outside atmosphere materials from invading into the tube.A positive pressure keeping means absorbs fluctuation of the pressure of the liquid food in the tube below the pressure flange, and prevents the liquid food pressure from dropping in negative pressure to keep the pressure of the liquid food in the tube below the pressure flange a positive pressure.