PURPOSE: To prevent breakage trouble by a method wherein a magnetic circuit is formed in a clearance between the lower and upper covers and a runner and the machine is assembled by attracting magnetic fluid to the clearance by the magnetic circuit.

CONSTITUTION: The annular clearance, which serves as a sealing part, is provided between the lower cover 21 and a runner band 22 of a magnetic body. The magnetic fluid 24 is attracted to this clearance. A magnet 25 is provided on the lower cover 21 for the annular clearance. Annular protuberances 27 are provided on the runner band 22 in order to increase a flux density. The magntic circuit 28 is formed by these constitutinos and the magnetic fluid 24 is attracted to the clearances of the magnetic circuit 28, therefore, it is not necessary to reduce the distance of the clearance at the sealing part and the breakage trouble of the hydraulic machine may be prevented.