A confluence control system comprising: a first variable flow rate control device capable of discharging liquid into a first discharge line with control over a flow rate of the liquid, a second variable flow rate control device capable of discharging liquid into a second discharge line merging with the first discharge line, with control over a flow rate of the liquid, a check valve that is provided in the second discharge line so that flow from the second variable flow rate control device to the first discharge line is in a forward direction, a pressure sensor for detecting a pressure in the first discharge line, a pressure flow rate control unit that is configured to receive one pressure command (Pi), one flow rate command (Qi), and a signal representing a detected pressure from the pressure sensor and to output an operation quantity (Vq) required for obtaining a pressure and a flow rate according to the pressure command (Pi) and the flow rate command (Qi), and an operation quantity distribution unit that is configured to receive the operation quantity (Vq) from the pressure flow rate control unit, and to produce first and second velocity signals (V1 and V2) on basis of the operation quantity (Vq) by dividing the operation quantity (Vq) and to output the first and second velocity signals to the first and second variable flow rate control devices (1 and 2) so that the first variable flow rate control device discharges liquid with a flow rate continuously changing according to the operation quantity (Vq) and so that the second variable flow rate control device does not discharge liquid, when the operation quantity (Vq) is not larger than a predetermined set value, or to produce the first and second velocity signals (V1 and V2) on basis of the operation quantity (Vq) by dividing the operation quantity (Vq) and to output the first and second velocity signals to the first and second variable flow rate control devices (1 and 2) so that the first and second variable flow rate control devices (1 and 2) respectively discharge liquid with a total flow rate continuously changing according to the operation quantity (Vq), when the operation quantity (Vq) exceeds the set value, wherein the pressure flow rate control unit limits a value calculated by a pressure control computation based on the pressure command (Pi) and the signal representing the detected pressure from the pressure sensor so that the value does not exceed a value according to the flow rate command (Qi). a first variable flow rate control device capable of discharging liquid into a first discharge line with control over a flow rate of the liquid, a second variable flow rate control device capable of discharging liquid into a second discharge line merging with the first discharge line, with control over a flow rate of the liquid, a check valve that is provided in the second discharge line so that flow from the second variable flow rate control device to the first discharge line is in a forward direction, a pressure sensor for detecting a pressure in the first discharge line, a pressure flow rate control unit that is configured to receive one pressure command (Pi), one flow rate command (Qi), and a signal representing a detected pressure from the pressure sensor and to output an operation quantity (Vq) required for obtaining a pressure and a flow rate according to the pressure command (Pi) and the flow rate command (Qi), and an operation quantity distribution unit that is configured to receive the operation quantity (Vq) from the pressure flow rate control unit, and to produce first and second velocity signals (V1 and V2) on basis of the operation quantity (Vq) by dividing the operation quantity (Vq) and to output the first and second velocity signals to the first and second variable flow rate control devices (1 and 2) so that the first variable flow rate control device discharges liquid with a flow rate continuously changing according to the operation quantity (Vq) and so that the second variable flow rate control device does not discharge liquid, when the operation quantity (Vq) is not larger than a predetermined set value, or to produce the first and second velocity signals (V1 and V2) on basis of the operation quantity (Vq) by dividing the operation quantity (Vq) and to output the first and second velocity signals to the first and second variable flow rate control devices (1 and 2) so that the first and second variable flow rate control devices (1 and 2) respectively discharge liquid with a total flow rate continuously changing according to the operation quantity (Vq), when the operation quantity (Vq) exceeds the set value, wherein the pressure flow rate control unit limits a value calculated by a pressure control computation based on the pressure command (Pi) and the signal representing the detected pressure from the pressure sensor so that the value does not exceed a value according to the flow rate command (Qi).