A shaft-seal device for high-temperature fluid including a seal case (2) formed as a metallic cylindrical structure of a single unit and comprised of a main body portion (2a, 2b, 2c), first and second holding portions (2d, 2e), first and second partition portions (2f, 2h), a channel formation portion (2g) forming a minute annular channel (27) with the outer circumference surface of a rotary shaft (1), and an o-ring holding portion (2i). The seal case is installed in an apparatus housing (8) with first and second o-rings (2m, 2n) in between. The intra-seal case region (A1), in which sealing rings (31, 32, 41, 42, 51, 52) of mechanical seals (3, 4, 5) are provided, and the high-temperature fluid region, which is an intra-apparatus housing region (A), are partitioned by a cooling chamber (28) into and from which coolant (82) is supplied and discharged via feed/discharge coolant paths (80, 81).