disposed in such a manner that the closed end of the cap 4 is on the upstream side of the extracting aperture 3 with a spacing therefrom while the open end 5 of the cap 4 faces the downstream side of the extracting aperture 3 the cap thus disposed is for utilizing a phenomenon that minute particles with certain mass have a larger inertia than that of the exhaust gas and the moving direction of the minute particles are difficult to change more particularly the minute particles in the exhaust gas are accelerated at the outer peripheral wall of the cap 4 by the venturi tube effect and if thus accelerated minute particles are to enter the extracting aperture 3 they are required to make a 180 u00b0 turn before such entry by this arrangement it is made difficult for the minute particles to enter the aperture 3 the embodiments of fig1 through 3 have the extracting apertures 3 directed toward the upstream so as to require more turning of the exhaust gas before entering into the egr pipe 2 as compared with the embodiment of fig4 having the extracting aperture 3 directed toward the downstream of the exhaust gas in the pipe 1 with the embodiment of fig2 the shape of the cap 4 39 is such that the minute particles are accelrated in outward directions centrifugal directions so as to effect.