A magnetic field generator comprises a pair of pole-piece units. The pair of
pole-piece
units respectively include plate yokes. Each of the plate yokes includes a surface
facing the other's and provided with a permanent magnet group and a pole piece.
The pole piece includes an annular projection having a plurality of annular-projection
pieces and a permanent magnet for reduction of magnetic flux leakage installed
on an outside surface of each annular-projection piece. The permanent magnet for
reduction of magnetic flux leakage may be disposed with a magnetizing direction
thereof being slanted with respect to a main surface of the permanent magnet group.
