To provide a locking structure of a valve which can maintain a set flow by preventing a valve element from moving.

The locking structure C of a valve which is attached to a flow controllable valve 1 includes a body part 7 in which a flow passage is formed, a valve element part 5 installed to be advanced into and retreated from the flow passage, a handle part 4 which is rotated to adjust the advanced and retreated amounts of the valve element part, and a rotation prevention member 8 for preventing the relative rotation of the body part 7 to the handle part 4. The locking structure further includes a valve stem part 2 which is connected to the valve element part 5 and in the outer periphery of which a male screw groove 23 is formed, a sleeve part 3 which is fixed to the handle part 4 and in which a female screw groove 36 threaded with the male screw groove 23 is formed, a distance holding mechanism 10 for holding constant the distance between the sleeve part 3 and the body part 7, and a co-rotation prevention mechanism 11 for preventing the valve stem part 2 and the sleeve part 3 from co-rotating.