PURPOSE: To improve the low-speed performance of an exhaust turbine supercharger, by radially swingably supporting the tip of tongue part of the vaneless scroll of the tubrine.

CONSTITUTION: When a solenoid 7 is energized, an iron core 6 is attracted rightward and the tongue part 3 is swung through an arm 5 so that the tip of the tongue part comes into a position A. When the energization of the solenoid 7 is stopped, the tongue part 3 is returned to the original position B by a return spring 8. When the solenoid 7 is de-energized under the slow operation of internal combustion engine, the tongue part is in the position B and the turbine torque increases and the rotary speed of the turbine rotor 13 rises. As a result, the supercharged pressure is heightened by the impeller 12 of compressor, the quantity of injected fuel is increased and the torque characteristics of the internal combustion engine are improved.