PURPOSE: To restrain heat conduction between casings themselves by disposing respectively carved legs on the coupled surfaces of casings themselves giving thermal deformation to each other while mounting respective keys in respective key ways of the carved legs by respective bolts.

CONSTITUTION: In a device for mounding casings themselves effecting thermal deformation to each other in a rotary machine, keys 2 are mounted respectively in key ways 12a with hexagonally apertured bolts 7 which key way 12a is provided in a carved leg 6a on the lower wheel chamber 4 side of the gear case side. Also, a swirl chamber 1 uses the swirl chamber 1 side carved leg 6d and is secured to the lower wheel chamber 4 side carved leg 6a by a bold 8. The respective key ways 12a, 12b of carved legs 6a, 6b are set such that radial lines centering around the core of the swirl chamber 1 coincide with the longitudinal center lines of the leys 2. Thus, the swirl chamber 1, while maintaining the core in the thermal deformation, slides on the mating surfaces of respective carved legs 6a, 6b so that it deforms radially.