An experimental system of the Couette type flow with a rotating disk has been designed to apply wall shear stress quantitatively on the cell culture at the microscopic observation in vitro. The shear stress on the wall is calculated with an estimated Couette type of the velocity profile between the rotating disk and the culture plate. The constant rotational speed (lower than 400 rpm) produces the wall shear stress lower than 2 Pa. The rotating disk system is mounted on the stage of an inverted phase contrast microscope to observe the behavior of cells adhered on the plate under the shear flow. Two kinds of cells were used in the test: C2C12 (mouse myoblast cell line), and MC3T3-E1 (mouse osteoblast precursor cell line). The experiments show that C2C12 tends to make orientation diagonal to the stream line, and that MC3T3-E1 tends to make orientation parallel to the stream line. Deformation and exfoliation of cells can be observed under controlled wall shear stress by the experimental system.