The aerodynamic drag acting on freestream-aligned circular cylinders with fineness ratios of less than 0.50 was measured using the 0.1 and 0.3 m magnetic suspension and balance systems. (MSBSs) The objectives of this study are to investigate the drag coefficient of a low-fineness-ratio circular cylinder and to find a critical geometry, where the drag coefficient becomes the local maximum. Since the model-position-sensing subsystem of the MSBS at Tohoku University had difficulties in testing a low-fineness-ratio model, we have developed a new model-position-sensing method. Using the new method, we measured the drag coefficients of circular cylinders with a fineness ratio from 0.30 to 0.50 at Reynolds number of 4.0 × 104-8.0 × 104 which is based on the model diameter. The results showed that the drag coefficient was almost constant in the test cases. From the trend of the drag coefficient, we concluded that the drag coefficients of circular cylinders with low fineness ratios can converge to the drag coefficient of the circular disk, without the critical geometry. Furthermore, we studied the unsteady aerodynamic drag. It is identified that the recirculation bubble pumping causes low-frequency drag fluctuations.