To rapidly start up a turbine by causing efficient inflow of exhaust gas to a turbine during low rotation of an engine.

When a nozzle blade angle is minimized in a state that an engine is run at a low rotation speed and an exhaust gas amount is low, a gap between the tip of a scroll casing tongue part 4 and the front edge of a nozzle blade 2 located rearmost the tip of the tongue part is reduced and leakage of exhaust gas to an inlet part 9 is suppressed. Further, when a rotation speed is high, an exhaust gas flow rate is high, and a nozzle blade angle is maximized, the outside surface of a tongue part is smoothly connected to the front edge of a nozzle blade and the increase of exhaust resistance is suppressed.