To rapidly respond to the application and release of braking force.

At the release of braking force, a non-excitedly operant permanent magnetic braking device at first overexcites a coil 20 at a preset period of time with a second power source 26, and then excites with a first power source 21. At the application of braking force after the cancel of electrification to the coil 20, the braking device reversely excites the coil 20 at a preset period of time to cancel the residual magnetic flux at the electrification to the coil. In stead of the reverse excitation, a capacitor which is charged at the normal excitation of the coil can be provided to cancel the residual magnetic flux developed at the excitation of the coil by means of the discharge of electric charge in the charged capacitor, at the application of braking force after the cancel of electrification to the coil. The coil may be used in single or in plural.