PURPOSE: To facilitate center alignment of a piston ring which is used for shaft sealing by improving setups around the center hole of a heat shroud which is provided between a turbine wheel and a center housing in which a piston ring is fitted for shaft sealing.

CONSTITUTION: The shaft sealing device is so constructed that the heat shroud 8 for heat shielding is provided between the center housing 5 equipped with bearings and the turbine wheel 1. The shaft 2 connected to the turbine wheel 1 is provided with a piston ring 4 as shaft sealer which is fitted into a groove 3 on the shaft and is put through the hole 7 of the center housing 5. Let S=gap between members 8 and 5 along radius; d=inside diameter of center hole 9 of member 8; and d'=free outside diameter of member 4. Then, set up relations among these to be 2S≥d-d'. Moreover, let T'=distance between end of the center hole 9 on housing side and end of hole 7 on shroud side; and T=axial length of member 4. Then, establish relation as T>T'.