To provide a braking device utilizing electroviscous fluid, capable of reliably holding a required braking force until a vehicle is halted.

A braking device has a fluid case 1 filled with electroviscous fluid 3 which changes its viscosity depending on a voltage applied thereto from the outside, and a rotation plate 2 inserted into the electroviscous fluid 3 in the fluid case 1. A voltage is applied to the electroviscous fluid 3 through the fluid case 1 and the rotation plate 2 to brake the rotation plate. The braking device further has a voltage controller 8 for raising a voltage depending on the rotating speed of the rotation member which is decreased by a voltage applied thereto. The voltage controller 8 calculates a voltage V to be applied to the electroviscous fluid on the basis of a signal from a sensor 10 for sensing the leg power (p) to a brake pedal 9 and a signal from a sensor 11 for sensing the rotating speed of the rotation plate 2, and instructs a high voltage generator to apply the same voltage V.