To eliminate of an attachment such as root stuck in an EGR pipe so as to hold a stable performance by opening an EGR valve in a prescribed engine operating region, and providing a control means for opening a switching valve to a bypass passage side.

An EGR pipe 1 is connected to between an intake passage 5 and an exhaust passage 7 in a diesel engine 3. In the EGR pipe 1, an EGR valve 9 is mounted in the vicinity of a part connected to the exhaust passage 7. When the operating condition of the engine 3 is in an operating region having a high exhaust temperature, the EGR valve 9 is opened through an actuator in a CPU 11. Since a switching valve 17 is opened to a bypass passage 15 side, a part of high temperature exhaust gas flows down from the EGR pipe 1 to the exhaust passage 7 through a bypass passage 15, and an attachment such as root stuck on an inner wall of the EGR pipe 1 is burning-eliminated by exhaust gas having a high temperature. It is thus possible to prevent change of an EGR ratio to be set, and corrosion of the EGR pipe, and it is also possible to hold a stable performance.