A form-fill-seal machine is configured to adjust for changes in the thickness of bags within a short time, and is provided with seal jaws, gas removal members, an air cylinder, and a control unit. The seal jaws transverse-seal a cylindrical film in a widthwise direction forming a bag. The gas removal members come into contact against the bag prior to transverse sealing of an upper edge part, discharging a gas upward from the bag. The air cylinder moves the gas removal members, switching the position of the gas removal members between a first position and a second position with respect to the seal jaws. The control unit, in a time slot just prior to the start of a transverse sealing action performed by the seal jaws, changes the timing of switching between the first position and the second position, and adjusts the amount of gas discharged from the bag.