wheels 15 a and 15 b of the low pressure turbine lt drives the compressor wheel 13 of the low pressure axial flow compressor lc as the high pressure turbine wheel 9 and low pressure turbines 15 a and 15 b are driven by the jet pressure of the combustion gas the engine 1 continues its rotation according to a negative feedback balance between the amount of fuel supply and the amount of intake air at the normal operating rotational speed as illustrated in fig2 in greater detail support parts of the bearing 5 f supporting the front end of the outer shaft 7 and the bearing 6 f supporting the front end of the inner shaft 8 are provided in the front bearing box 21 at a certain distance from each other in the axial direction as illustrated in fig3 in greater detail support parts of the bearing 5 r supporting the rear end of the outer shaft 7 and the bearing 6 r supporting the rear end of the inner shaft 8 are provided in the rear bearing box 25 at a certain distance from each other in the axial direction floating ring seals 31 a and 31 b are provided ahead of the front bearing 6 f of the inner.