A leaf spring valve which is capable of being opened and closed assuredly and stably with a small operating torque by having a stored springing force in a valve disc itself, reducing a cost, and being manufactured compact, and being excellent in durability and high in practical use value, and which further provides a constant flow function to the valve disc itself having a sealing function for multi-functionability, provides various types of constant flow functions according to the number of rotations of the spring, and can controllably open and close a flow path for fluid, wherein one end of a main spring (47) is installed inside a valve chamber (42) of a valve box (41), the other end is installed on a valve stem (52) in the valve chamber (42), the side face of the main spring (47) is disposed opposedly to and pressingly against a valve seat (42a) of the valve box (41), and the valve stem (52) is rotated by an actuator (55) to displace the main spring (47) toward the center of the valve stem (52), whereby the side face of the main spring (47) is moved apart from the valve seat (42a) to open a secondary side flow path port (44).