PURPOSE: To enhance the effect of supercharger in a low speed range by dividing the inside of a turbine scroll into two scroll chambers with the use of a partition wall, and by extending the inlet part of a turbine impeller in one of nozzle parts formed respectively in these scroll chambers, which is used in a low speed range.

CONSTITUTION: A turbine scroll 4 of an exhaust turbine impeller is divided into a two scroll chambers 4a, 4b by a partition wall 5 which also divides a nozzle section into two nozzle parts 6a, 6b. The part 1b of the inlet part of a turbine impeller 1, which faces the scroll chamber 4b, has a shape such that it extends in the nozzle part 6b. Further, the partition wall 5 is connected to a partition plate 8 in a turbine inlet 7, and a control valve 12 is provided in an aperture 11 which is formed in the partition plate 8 so as to communicate between an open scroll 9 and a closed scroll 10. Further, a bypass valve 22 is provided in a bypass aperture 21 formed in a closed scroll 22 downstream of a control valve 12.