In an assembly method of a magnetic fluid seal (100) that includes a magnetic field forming member (130) divided in a circumferential direction, a magnetic pole member (120) including a pair of magnetic fluid retaining portions (121, 122) and a coupling portion (123) that couples them, a first bearing (160) and a second bearing (170), a step of fixing the first bearing (160) to a shaft (400) in a state in which the shaft (400) is directed in a vertical direction, a step of attaching the magnetic pole member (120) from above the first bearing (160), a step of fixing the second bearing (170) to the shaft (400) from above the magnetic pole member (120) to thereby fix the magnetic pole member (120) in a state in which the magnetic pole member (120) is positioned with respect to the shaft (400); and a step of attaching the magnetic field forming member (130) between the pair of magnetic fluid retaining portions (121, 122) are performed in order.