PROBLEM TO BE SOLVED: To prevent a magnetic fluid from flowing out from a magnetic seal mechanism to an object to be sealed without restraining a rotary shaft.SOLUTION: A magnetic seal mechanism comprises: a magnetic collar 7 which is fitted to an outer periphery of a pinion gear 3, and whose outer shape has a cylindrical part 71； an annular magnet 8 disposed on an outer peripheral surface of the cylindrical part 71 of the magnetic collar 7 at an interval； and a magnetic fluid 10 forming a magnetic circuit on the outer peripheral surface of the cylindrical part 71 with the magnet 8 and the magnetic collar 7 and held between the magnet 8 and the magnetic collar 7. On an outer peripheral surface of the magnetic collar 7, a groove part 72 is formed over the entire periphery in a circumferential direction and a flange part 73 whose outer diameter is larger than the outer diameter of the cylindrical part 71 is formed over the entire periphery in the circumferential direction.SELECTED DRAWING: Figure 2【課題】回転軸を制約することなく、磁気シール機構からシールする対象に磁性流体が流出するのを防止する。【解決手段】ピニオンギア３の外周に嵌合される、外形が円筒部７１を有する磁性カラー７と、磁性カラー７の円筒部７１の外周面に間隙を空けて配置される環状の磁石８と、円筒部７１の外周面で、磁石８および磁性カラー７で磁気回路を形成し、磁石８と磁性カラー７との間に保持される磁性流体１０と、を備え、磁性カラー７は、外周面に、周方向の全周に亘る溝部７２、および、周方向の全周に亘って外径が円筒部７１の外径以上であるフランジ部７３、が形成されている。【選択図】図２
