PURPOSE: To prevent fluid leakage at a connection part in a device to connect a body having a flowing port and a valve and a driving part to each other.

CONSTITUTION: A ring installation part 5a is formed on a body 5. On an installation side surface 19 of the installation part 5a, an O ring 18 is fit. A surface on the outer periphery of the O ring 18 of the installation side surface 19 is formed of an installation surface 19b partially formed against the peripheral direction and a sink surface 19c forming a part except for the installation surface 19b on a surface which is lower than the installation surface 19b.