Abstract: A seal device for a rotary heat-exchanger of a gas turbine is held in bearing contact with each end face of a regenerative rotor of the heat-exchanger to partition a low-pressure exhaust gas passage and a high-pressure air passage from one another and to seal therebetween. The regenerative rotor is rotated across the passages to effect the heat-exchanger between the low-pressure exhaust gas and the high-pressure air. The seal device comprises a bellows having one end thereof secured to a seal member rotatably supporting the regenerative rotor and the other end secured to a flange fast on the inner wall of the rotor housing, and a jacket substantially backing up the bellows to control the shape thereof.