To provide an EGR diffusion unit in which the flow velocity of an EGR gas that is dispersed an supplied into an air intake passage from the circumference thereof is controlled to suppress the concentration irregularity of the EGR gas in the air intake passage.

The EGR diffusion unit 1 includes: an outer circumferential passage 7 for covering the outer circumference of the air intake passage 5; an EGR inlet 8 for supplying the EGR gas to the outer circumferential passage 7; a plurality of EGR outlets 9 which introduce the EGR gas existing in the outer circumferential passage 7 into the air intake passage 5, and the plurality of EGR outlets 9 are arranged dispersedly in the circumferential direction of an internal tube 41; and a flow passage resistance setting means (baffle plate 11, the passage length of an outlet passage 12 or the like) for increasing the flow passage resistance of the EGR outlet 9 on the side closer to the EGR inlet 8 and for decreasing the flow passage resistance of the EGR outlet 9 on the side farther from the EGR inlet 8 so that the flow velocities of the EGR gasses supplied from the plurality of EGR outlets 9 to the air intake passage 5 are made uniform. As a result, the concentration irregularity of the EGR gas in the air intake passage 5 can be suppressed and emission can be prevented from getting worse.