An exhaust reflux device for an internal-combustion engine provides a technology ensuring accurate calculation of both a low-pressure EGR ratio and a high-pressure EGR ratio, flow rate control for both a low-pressure EGR passage and a high-pressure EGR passage which is configured as a closed-loop control, stabilized intake temperature and charging pressure, and reduced degradation in exhaust emission and motive power performance. The exhaust reflux device calculates a low-pressure EGR ratio representing a ratio of the amount of low-pressure EGR gas to the amount of intake air sucked by the internal-combustion engine and a high-pressure EGR ratio representing a ratio of the amount of high-pressure EGR gas to the amount of intake air using CO2 concentration at an air-intake passage at the downstream of a connecting location of the low-pressure EGR passage and at the upstream of a connecting location of the high-pressure EGR passage, CO2 concentration at an air-intake passage at the downstream of the connecting location of the high-pressure EGR passage, and concentration of CO2 discharged by the internal-combustion engine (S103), and controls calculated values of the low-pressure EGRratio and high-pressure EGR ratio to be respective target values (S104).