A magnetic fluid seal is provided, capable of producing a stable scaling performance by stably holding magnetic fluid in place between two members, even in cases when the two members become eccentric. The magnetic fluid seal includes: an annular magnetic circuit forming member that is disposed on a housing; an annular member that is disposed on a shaft; and a magnetic fluid that is magnetically held between axially opposing surfaces of the magnetic circuit forming member and the annular member. In addition, the annular member comprises a flexible member that is swayable so that a portion of the annular member that opposes the magnetic circuit forming member follows the magnetic circuit forming member.