To make easy mounting/demounting of each valve by lowering the mounting position of a repairing valve (wafer type butterfly valve) on a fluid transport pipe line for decreasing the mounting depth in a manhole through holding the wafer type butterfly valve with a plate flange to a flange part of the line as well as fixation of an air valve to a plate flange.

A fixation bolt 15 is inserted in from a bolt through hole of a plate flange 2, and it is made to penetrate a bolt insertion hole of a wafer type butterfly valve 1 and a bolt insertion hole of a flange part 10 on a fluid transport pipe line 9, in order, and fixed by a nut 20. Since an upper surface 21 of the flange 2 is held flat at this time, the fixation to an air valve 3 is made easy and the good seal performance can be assured. The air valve 3 is made to abut on the upper surface 21 via a gasket 22, then a fixation bolt 16 is inserted into a bolt insertion hole 23 of the valve 3, and threadwise engaged with a nut 17 embedded in a bottom face through the bolt insertion hole of the flange 2, thereby fixing the valve 3.