PURPOSE: To generate a high braking torque by introducing a fluid to a working chamber or discharging the fluid from the chamber by slits provided or at least one of a rotor wheel or a stator wheel.

CONSTITUTION: Introducing a fluid into a working chamber 10 and discharging the fluid from the working chamber 10 are permitted through at least one of a rotor wheel 3 and a stator wheel 2, for instance, through slits 8, 9 provided drilled at a side of the rotor wheel 3. The slit 8 for introducing working fluid is located at the radially inner region, and the slit 9 for discharging working fluid is located at the radially outer region. The wheels 2, 3 are connected to passages for introducing the working fluid and for discharging the working fluid without having a thickness part influencing the flow. The both wheels 2, 3 have comfortable contour shapes in a manner that the flow can be obtained from one wheel to the other wheel without any impact.