PURPOSE: To prevent adhesion of carbon to the seat sections of a valve element and a seat, by providing an air passage for blowing out air to the seat sections to clean the latter, and by disposing a shut-off valve for opening and closing the air passage.

CONSTITUTION: When the degree of vacuum introduced into a vacuum chamber 13 exceeds a pressure at which a flow control valve 9 is opened, a shut-off valve 31 is opened, and therefore air is introduced into an intake-air system 1 through a conduit 30, a passage 26, an annular groove 28 and an air passage 26 due to the negative pressure in the intake-air system. Then, air passing through the air passage 26 increases its flowing velocity since the flowing sec tional area of the passage 26 is gradually decreased, and therefore, is powerfully blown onto the seat section of a valve element 19 and a seat 21 so that carbon, etc. adhered to the sections are blown off. Further, when a predetermined time elapses after the opening of the shut-off valve 31, a delay mechanism closes the shut-off valve 31, and therefore, it is possible to prevent air in an excessive amount from mixing into recirculated exhaust gas.