The Yamanashi Maglev system has two types of main braking systems: regenerative braking system (primary brake using electrodynamic power) and on-board mechanical braking system (backup brake). The mechanical backup braking system is installed on vehicles. It is used to safely and accurately stop the vehicle in case the electrical braking system has failed. On the Yamanashi Maglev Test Line, an aerodynamic braking system is used as an element of the mechanical backup braking system. In the aerodynamic braking system, braking force is obtained by aerodynamic drag which is generated by unfolded brake panels. The aerodynamic brake is very effective in high speed operation, because the aerodynamic drag is proportional to the square of vehicle speed. This paper reports the aerodynamic brake system and results of running tests on the Yamanashi Maglev test line.