PURPOSE: To provide a valve of simple structure capable of adjusting the very small flow rate.

CONSTITUTION: The butterfly valve structure is employed, and an elliptical valve plate 43 is turned inside a rubber sleeve 41. A pair of gate parts 56, 56 are provided on the inner circumferential surface of the sleeve 41, and the surfaces 57, 57 of these gate parts 56, 56 and the outer circumferential edge of thc valve plate 43 are freely brought close to each other. When the opening of the valve plate 43 is small, a small passage of slit shape is present between this valve plate 43 and the respective surfaces 57, 57. Thus, the very small flow rate can be realized.