Numerical calculations by a finite-difference method were made for a steady three-dimensional flow inside a cylindrical housing when a disk having radial slits and its housing were rotated. Three types of flows for the following conditions were examined at the same relative angular velocity between them: (1) The slitted disk rotated and the housing was stationary. (2) The slitted disk and the housing rotated in opposite directions. (3) The slitted disk was stationary and the housing rotated. With the increase in the relative angular velocity, the difference in flow inside the housing due to the rotating conditions becomes pronounced. For the counter-rotating condition, the radial flow induced inside the housing was suppressed and the tangential velocity distribution tended to be linear, showing the smallest torque transmitted between the disk and the housing.