We clarified the characteristics of rotating-disk and rotating-concentric-cylinder braking device types using ERF (electro-rheological fluid) with smectite particles. Concerning the steady characteristics of the both braking devices, the current density of the rotating-disk type is smaller than that of the concentric cylinder type. In addition, the input electric power per increment of torque has the same ratio as the enhancement of the shear rate. In contrast, regarding the transition characteristics, the rise time of the torque for the rotating-disk type is shorter than that for the concentric-cylinder type, though the current’s rise time is almost the same in both braking devices. It can be considered that the current density of the rotating-disk type is small and the rise time of the torque of the one type is small due to the influence of the secondary flow. The microscopic tendency of the electric charge can be guessed from the transition characteristic of the electric current.