Flow-rate adjustable valve

A flow-rate adjustable valve for adjusting a flow rate of liquid flowing through a flow path, the flow-rate adjustable valve comprising:

• a main valve body movably supported in the flow path via a diaphragm membrane,
• a back pressure chamber in which liquid supplied from an upstream side of the flow path at a predetermined pressure is contained and a biasing force is generated in a valve-closing direction for closing the main valve body by the supplied liquid,
• a plurality of inlet holes communicating the upstream side of the flow path with the back pressure chamber,
• an outlet hole communicating a downstream side of the flow path with the back pressure chamber, and
• a pilot valve body for opening and closing the outlet hole,
• wherein
• moments acting on the main valve body based on the liquid flowing into the back pressure chamber through the plurality of inlet holes are canceled by each other in total, under a condition in which the pilot valve body opens the outlet hole.