A composite valve comprising: a first valve body; a valve shaft which is provided with a second valve body; an elevation driving means for moving up and down said valve shaft; a pilot valve body which is driven so as to be opened and closed by utilizing an elevating motion of said valve shaft; and a valve main body which is provided with an inflow port and an outflow port, wherein between said inflow port and said outflow port in said valve main body, there are provided a fitting and inserting chamber to which said first valve body is slidably fitted and inserted, and which is zoned into a back pressure chamber and a first valve chamber by said first valve body, a first valve port which is open to said first valve chamber, a second valve chamber in which said pilot valve body and the second valve body are arranged so as to be movable up and down, a communication path which communicates said inflow port or the first valve chamber with said second valve chamber, a second valve port which communicates said second valve chamber with said outflow port, and a pilot passage which communicates said back pressure chamber with said outflow port, and wherein in the case that a lift amount of said second valve body is 0, said second valve port is closed by said second valve body, wherein in the case that the lift amount of said second valve body is equal to or less than a predetermined amount, said pilot passage is closed by said pilot valve body, and said first valve port is closed by said first valve body, thereby taking a small flow rate control state in which a flow rate is controlled in correspondence to the lift amount of said second valve body, and in the case that the lift amount of said second valve body goes beyond said predetermined amount, said pilot valve body is moved up in conjunction with the upward movement of said valve shaft so as to open said pilot passage, thereby taking a large flow rate control state in which said first valve body opens said first valve port on the basis of this. a first valve body; a valve shaft which is provided with a second valve body; an elevation driving means for moving up and down said valve shaft; a pilot valve body which is driven so as to be opened and closed by utilizing an elevating motion of said valve shaft; and a valve main body which is provided with an inflow port and an outflow port, wherein between said inflow port and said outflow port in said valve main body, there are provided a fitting and inserting chamber to which said first valve body is slidably fitted and inserted, and which is zoned into a back pressure chamber and a first valve chamber by said first valve body, a first valve port which is open to said first valve chamber, a second valve chamber in which said pilot valve body and the second valve body are arranged so as to be movable up and down, a communication path which communicates said inflow port or the first valve chamber with said second valve chamber, a second valve port which communicates said second valve chamber with said outflow port, and a pilot passage which communicates said back pressure chamber with said outflow port, and wherein in the case that a lift amount of said second valve body is 0, said second valve port is closed by said second valve body, wherein in the case that the lift amount of said second valve body is equal to or less than a predetermined amount, said pilot passage is closed by said pilot valve body, and said first valve port is closed by said first valve body, thereby taking a small flow rate control state in which a flow rate is controlled in correspondence to the lift amount of said second valve body, and in the case that the lift amount of said second valve body goes beyond said predetermined amount, said pilot valve body is moved up in conjunction with the upward movement of said valve shaft so as to open said pilot passage, thereby taking a large flow rate control state in which said first valve body opens said first valve port on the basis of this.