PURPOSE: To obviate the need of a cooling device and obtain a desired brake power for an internal combustion engine by connecting a throttle quantity adjusting means for adjusting the throttle quantity according to the air flow rate in an air passaged, with a throttle valve installed in the air passage of a turbine.

CONSTITUTION: When a vane wheel 31 is revolution-driven by a turbine shaft 15, the energy for compressing air onto the vane wheel 31 is consumed, and the consumed energy generates a brake power for controlling the driving system of a vehicle. In the first stage, the compressed air is discharged into a discharge passage 37, and when the discharge is gradually increased, the flow speed of the compressed air is increased, since the sectional area of the discharge passage 37 is constant, and a negative pressure gradually acts onto a negative pressure actuator 44 which constitutes a throttle adjusting means 43. Therefore, the negative pressure actuator 44 gradually turning-operates a throttle valve 41 in the closing direction and suppresses the air quantity supplied into the vane wheel 31. Therefore, the load of the vane wheel 31 is reduced, and the brake power for the driving system of the vehicle can be restricted to a constant value.