Abstract: In an exhaust gas recirculation system of the type including a control valve inserted in an exhaust gas recirculation passageway for controlling the flow rate of the exhaust gases to be recirculated, a constant pressure chamber defined in the recirculation passageway upstream of the control valve, and a modulator valve with a diaphragm chamber in communication with the constant pressure chamber for controlling, in response to the pressure variation in the diaphragm chamber, the negative pressure which is transmitted to the control valve for operating the same, an orifice is interposed between the constant pressure chamber and the diaphragm chamber and is so contoured that the resistance to the flow from the diaphragm chamber to the constant pressure chamber is greater than the resistance to the flow from the constant pressure chamber to the diaphragm chamber.