To provide a valve having a movable face making no direct contact with a flow medium so as to secure a maximum valve operation efficiency even when using an irritable medium.

In a channel 16 of a housing 10, a diaphragm 36 seals a cylindrical chamber 48 from a medium inside the channel 16, while a disc 44 arranged in one end of a sleeve 40 divides the cylindrical chamber 48 into small chambers 50, 52. According to a shift of the sleeve 40, the other end face 42 is forcibly pressed to a guiding face 34 in a flow main body 18, and tight sealing in a valve can be secured by a ring-shaped sealing face 58 based on the diaphragm 36.