A magnetic seal device that includes a magnetic sleeve having a cylindrical body that and fits on an outer peripheral surface of a rotatable shaft, a ring shaped magnet being arranged radially outwardly from an outer peripheral surface of the magnetic sleeve with a gap, and a magnetic circuit formed between the outer peripheral surface of the magnetic sleeve and the ring shaped magnet. A magnetic fluid is maintained at the gap. The magnetic sleeve includes a groove arranged circumferentially around the outer peripheral surface of the magnetic sleeve, and a flange extending radially outwardly from and circumferentially around the outer peripheral surface of the magnetic sleeve. The flange has a diameter that is larger than a diameter of the outer peripheral surface of the magnetic sleeve.本發明之目的在於提供一種不會拘束旋轉軸，且防止磁流體自磁力密封機構流出至密封之對象。本發明之磁力密封機構包含：磁性軸環7，其嵌合於小齒輪3之外周，且外形具有圓筒部71；環狀之磁鐵8，其隔以間隙而配置於磁性軸環7之圓筒部71之外周面；及磁流體10，其於圓筒部71之外周面，被保持於形成磁路之磁鐵8與磁性軸環7之間；且磁性軸環7於外周面形成有遍及周向之整周之溝槽部72、及遍及周向之整周其外徑為圓筒部71之外徑以上的凸緣部73。
