To prevent the set characteristic of a leaf valve fixed to a valve seat member by tightening a piston nut from changing when the piston nut is locked.

In this fixing structure of the leaf valve, the leaf valve 1 seated on a valve seat member 2 is fixed with a fixing body 4 interposed in the tip faucet engagement part 3a of a rod body 3 passed through the axis part of the valve seat member 2. A press-fit body 5 press-fitted into a space part 3e formed in the axis part of the tip faucet engagement part 3a of the rod body 3 enlarges the outer diameter of the tip faucet engagement part 3a of the rod body while maintaining the inside of the space part 3e in a sealed state to fit it to the inner periphery of the fixing body 4.