An axial flow rotating machinery includes: a rotor; a casing; a rotating-blade stage including rotating blades and a radially-outer side rotating blade ring continuing to radially outer ends of the rotating blades; and a rotating-blade side seal device configured to seal a gap between the radially-outer side rotating blade ring and the casing. The rotating-blade side seal device includes: a seal fin having an annular shape and extending toward an outer peripheral surface of the radially-outer side rotating blade ring from the casing; and a swirl brake fixed to the casing in a cavity formed at an upstream side of the seal fin. The swirl brake includes: a first plate-shaped member having a surface along a radial direction of the rotor; and a second plate-shaped member or a third plate-shaped member having a surface oblique to the radial direction of the rotor.