To prevent an axial-flow turbine from becoming unrotative by sediment accumulated on an inner surface of a casing.

An exhaust gas turbine supercharger is constituted by fitting an end of a casing 3 forming an exhaust gas introduction port 2 and an end part of a nozzle part 5 connected to it on which other so that the nozzle part 5 is fitted on the end of the casing 3 from inside, structuring the casing 3 so that it is spread out by thermal expansion displacement in the diametrical direction of the nozzle part 5 transmitted to the end of the casing 3, spreading out the side of the casing 3 from inside by the thermal expansion displacement of the nozzle part 5 at an initial stage of engine starting by using behavior of the nozzle part 5 to thermally expand in advance of the casing 3 and devising it so that a blade head end is released from sediment even when the blade head end is fastened on an inner surface of the casing and so that an axial-flow turbine 4 can come out of a state where it is impossible to rotate.