Experiments on friction of parallel coaxial discs rotating in a cylindrical vessel with some surface roughness were carried out under various radial, axial clearances and disc intervals. The main results obtained are summarized as follows : (1) Resisting coefficient of a special single disc estimated as if each surface of the disc were facing the vessel surface fixed and rotated with same speed respectively, is larger than the value of an enclosed single disc. (2) Effects of radial clearance for resisting coefficient decrease with an increasing disc interval, and disappear when the ratio of disc interval to disc dia. is 0.6∼0.8.