1. A braking device for a moving body comprising a braking unit in which multiple magnetic poles each wound with a coil are arranged side by side in a moving direction of a movable object that is movable along a rail, and which is placed so that an interval is provided between the magnetic poles and the rail during traveling of the movable obj ect,
wherein, at the time of starting braking, the braking unit is configured with plural magnetic-pole sets which are each a set of adjacent magnetic poles in said multiple magnetic poles, and in which polarities of the adjacent magnetic poles are set to the same polarity but adjacent magnetic-pole sets in said plural magnetic-pole sets are set to have mutually different polarities; and thereafter, the polarities of the adjacent magnetic poles are set to mutually different polarities.
2. A braking device for a moving body comprising a braking unit in which multiple magnetic poles each wound with a coil are arranged side by side in a moving direction of a movable object that is movable along a rail, and which is placed so that an interval is provided between the

magnetic poles and the rail during traveling of the movable obj ect,
wherein the braking unit energizes half of the coils wound around each set of adjacent magnetic poles in said multiple magnetic poles, and thereafter, energizes all sets of adjacent magnetic poles to thereby change each set of adjacent magnetic poles to have mutually different polarities .
3. The braking device for a moving body according to Claim 1 or Claim 2, wherein, after the elapse of a preset time from starting to brake the movable object, the braking unit changes the polarities of said each set of adjacent magnetic poles to mutually different polarities.
4 . The braking device for a moving body according to Claim 1 or Claim 2, wherein the magnetic poles in the braking unit are provided with a device for changing the interval between the magnetic poles and the rail during braking operation from that before braking operation, and a detection unit for detecting their coming close to the rail, so that said each set of adjacent magnetic poles are changed to have mutually different polarities, on the basis of a signal from the detection unit.

5. The braking device for a moving body according to any one of Claims 1 through 4, wherein the magnetic poles during braking operation of the braking unit are provided with an adjusting part for adjusting the interval to the rail.
6. The braking device for a moving body according to any one of Claims 1 through 5, wherein the magnetic poles in the braking unit are provided with a brake pad on their side that will come close to the rail, and the brake pad is made contact with the rail when that side comes close thereto.

7 . The braking device for a moving body according to any one of Claims 1 through 5, wherein a coil group that causes no change of magnetic polar direction and a coil group that can cause inversion of magnetic polar direction are serially connected to each other, and circuit switchers are connected to both ends of the coil group that can cause inversion of magnetic polar direction, so that magnetic polar directions of the coil group that can cause inversion of magnetic polar direction are changed by contact-switching of the circuit switches.
8 . The braking device for a moving body according to any one of Claims 1 through 5, wherein a coil group that causes

no change of magnetic polar direction and a coil group that can cause inversion of magnetic polar direction are parallelly connected to each other, and circuit switchers are connected to both ends of the coil group that can cause inversion of magnetic polar direction, so that magnetic polar directions of the coil group that can cause inversion of magnetic polar direction are changed by contact-switching of the circuit switches.
9. The braking device for a moving body according to any one of Claims 1 through 5, wherein a coil group that can cause inversion of magnetic polar direction is connected inside a full bridge circuit of semiconductor switching elements, and a coil group that causes no change of magnetic polar direction is serially connected to the full bridge circuit, so that magnetic polar directions of the coil group that can cause inversion of magnetic polar direction are switched by operations of the switching elements.
10. The braking device for a moving body according to any one of Claims 1 through 5, wherein a coil group that can cause inversion of magnetic polar direction is connected inside a full bridge circuit of semiconductor switching elements, and a coil group that causes no change of magnetic polar direction is parallelly connected to the full bridge

circuit, so that magnetic polar directions of the coil group that can cause inversion of magnetic polar direction are switched by operations of the switching elements.
11. The braking device for a moving body according to any one of Claims 1 through 5, wherein a single module in which six semiconductor switching elements are incorporated is used, so that a coil group that causes no change of magnetic polar direction and a coil group that can cause inversion of magnetic polar direction are connected to a half bridge and a full bridge in that module, respectively.