In order to study aerodynamic characteristics of a carriage arm equipped on hard magnetic disks, water tunnel tests with 10 times enlarged model of an actual carriage arm were conducted under Reynolds number similitude, which allows the time scale of the tests to expand approximately 1300 times larger than that under actual condition in the air. In the tests, flow visualization around the carriage arm model with fluorescent dye injection and Laser-light sheet technique was carried out. Fluid dynamic drag, lift and torque on the model were also measured. Effects of incident flow velocity and incident flow angle were investigated.