Can be reliably prevented over a long period of time easily and the position shift and withdrawal from the permanent magnet groups of the permanent magnets and provide a magnetic field generator with good productivity. Pole pieces 16a provided on one main surface of the permanent magnet groups 14a permanent magnet groups 14a provided on the plate yoke 12a on, so as to form the exposed portion 18b, the magnetic field generator 10, so as to surround the permanent magnet groups 14a I comprises a Tsuba-jo member 36 provided on the pole piece 16a so as to cover the exposed portion 18b and the frame member 34 is provided in the plate yoke 12a on. Press bolt 44 which is screwed into the frame member 34 presses the outer peripheral surface 18a of the permanent magnet groups 14a through the interposition material 42 or directly. Press bolt 48 is screwed into Tsuba-jo member 36, presses the exposed portion 18b of the permanent magnet groups 14a through the interposition member 46 or directly. And configured in the same way also the plate yoke 12b side.永久磁石の永久磁石群からの離脱および位置ずれを簡単にかつ長期に亘って確実に防止でき、生産性のよい磁界発生装置を提供する。磁界発生装置10は、板状継鉄12a上に設けられる永久磁石群14a、露出部18bを形成するように永久磁石群14aの一方主面に設けられる磁極片16a、永久磁石群14aを囲むように板状継鉄12a上に設けられる枠状部材34、および露出部18bを覆うように磁極片16aに設けられる鍔状部材36を備える。枠状部材34に螺入された押しボルト44は、直接または介挿部材42を介して永久磁石群14aの外周面18aを押圧する。鍔状部材36に螺入された押しボルト48は、直接または介挿部材46を介して永久磁石群14aの露出部18bを押圧する。板状継鉄12b側についても同様に構成される。
