PURPOSE: To hold extremely high sealing capacity over a relatively long time span by using liquid with insoluble properties at least partially.

CONSTITUTION: A valve seat 10 of a valve 13 is provided with a magnetic fluid layer shown by 14, by two permanent magnets 271, 273, and a magnetic fluid sticks to the valve seat 10. In a valve part 11, a sealing device 12 can be laminated with a magnetic fluid 15, by a member 263 formed of magnetizable material. The magnetic fluids 14, 15 comprise suspension of extremely small grains of magnetic material in a viscous fluid and have such properties as to be insoluble in liquid that flows through the valve and further inert to connected liquid. With the valve seat 10 thus laminated and with the sealing device 12 in the valve part 11 with the magnetic fluids 14, 15, extremely high sealing action can be attained when the valve 13 is closed even if the valve seat 10 and the sealing device 12 have non-plane parts and the sealing device 12 has an aging phenomenon. When the valve part 11 is pressed by the valve seat 10, the magnetic fluid layers 14, 15 are deformed.