A gas turbine combustor includes multiple aft frames each having a floating seal that seals a gap between an aft frame and a gas turbine in inner and outer peripheries of the aft frame, and a side seal that seals a gap between the aft frames adjacent to each other in a circumferential direction, and a corner seal that is placed in a gap portion provided between corner portions of the aft frames adjacent to each other in the circumferential direction, seals air leaking from at least the gap portion into the gas turbine side, and is independent of the floating seal and the side seal.