PURPOSE:To provide a rotary heat exchanger in which no deterioration occurs at a seal part even if each of the parts constituting a seal device of the rotary type heat exchanger produces an error due to thermal expansion of uneven temperature distribution. CONSTITUTION:Four generally D-shaped openings arranged at a casing 4 are inlet and outlet ports for low temperature gas and high temperature gas. The low temperature gas and the high temperature gas are passed to a rotary heat accumulating type rotor arranged within the casing 4 without being mixed from each other so as to perform a heat exchanging operation. This invention relates to such a seal device for a rotary type heat exchanger constructed as above. The low temperature gas and the high temperature gas are separated within the casing 4 by a generally D-shaped seal member 9 comprises of a linear part and a curved part and a bellows with a generally D-shape and a V-shaped cross section contacting with an entire circumference of a seal member 9. When the outside part of the bellows 7 is kept at a higher pressure than that of the inner side, a guide member for preventing deformation of the bellows 7 is arranged at an outside part of the bent part connecting this linear part and the curved part as well as an inside part of the linear part of the generally D-shaped bellows 7. The wall thickness of the seal member 9 on the low pressure side may be thicker than that of the high pressure side.