. . . . "The respective switching valve 2 comprises a substantially cylindrical valve box 21 integrally formed with the header 1 made of a resin, a valve body 22 spherically formed from an elastic material such as silicone rubber, chloroprene rubber, ethylenepropylene rubber or the like, and held at one end side of the valve box 21, and a plate-like cover member 23." .