Fluid-controlled valve

A fluid-controlled valve, wherein pistons are mounted in an actuator via springs, the pistons allow a valve disk to contact with and separate from a valve seat to open and close a flow path by compressed air from air inlets or spring forces of the springs, the pistons are separately formed as a plurality of piston members, the separate pistons are arranged in a series state with respect to the valve seat in a spring state via the plurality of springs having different spring loads, the corresponding air inlets through which the compressed air that operates the corresponding separate pistons in directions opposite to spring directions of the springs is supplied are formed in the actuator, the corresponding separate pistons are disposed so that the compressed air from the corresponding air inlets or the spring forces of the corresponding springs cause the pistons to separately and independently ascend and descend in predetermined strokes in the actuator, and the valve disk is disposed so as to be able to seal the flow path by different sealing forces depending on descending states of the corresponding separate pistons formed as the plurality of piston members.