The falling drag test of circular cylinders was carried out in a low Reynolds number region in order to study the effects of cylinder length and plane side-walls on the drag of cylinders. From the data analysis based on the dimensional analysis method, it is shown that the drag coefficient of finite length circular cylinders is expressed by an empirical formula composed of the Tachibana-Iemoto expression in two dimensional theory and the correlation function of three variables (L/D, H/D and B/H). In the useful region of our formula, the drag of cylinders increases with an increase of the ratio of length to diameter (L/D) and a decrease of plane side-wall variables (H/D and B/H).