PURPOSE: To easily adjust the torque and sealing performance of a valve, already assembled and completed, without changing structural parts.

CONSTITUTION: A mainbody 1 is split into two, upper and lower, cut allowances 2 are provided for the split planes, an inclusion member 3 containing a spacer, a shim and a screw adjusting mechanism is inserted between the opposite split planes provided with the cut allowances 2 and the split mainbodies 1 are fastened with a fixing bolt 4. As the flatness of the inner diameter of the mainbody 1 is changed with the thickness of the inclusion member 3, the seating torque of an elastic seat ring 5 mounted on the inner face of the mainbody l and bitten into the peripheral face of a valve 7 can be reduced within a certain range and adjusted for higher sealing performance.