An exhaust treatment device for a diesel engine in which an exhaust flow divider is provided in an exhaust path, the exhaust flow divider causes an exhaust to flow an EGR gas with PM unevenly distributed and a remaining discharged gas 5 in a divided manner, the EGR gas 4 is recirculated to a combustion chamber 6, and the discharged gas is discharged to an atmospheric side, wherein a first corona discharge passage and a second corona discharge passage are provided at the exhaust flow divider, corona discharge in the first corona discharge passage causes the PM, water vapor, and oxygen in the exhaust to generate electron attachment, and electrostatic force causes the exhaust to flow the EGR gas with the electron-attached PM, water vapor, and oxygen unevenly distributed and the remaining discharged gas in a divided manner, the discharged gas is guided to the second corona discharge passage, corona discharge in the second corona discharge passage causes gas molecules in the discharged gas to dissociate, and NOx in the discharged gas is reduced to N 2, a center cylinder is disposed at a center part of the exhaust flow divider, an exhaust swirling passage is provided around this center cylinder, the exhaust swirling passage serves as the first corona discharge passage, the center cylinder serves as a negative electrode of the first corona discharge passage, an outer circumference wall of the exhaust swirling passage serves as a positive electrode of the first corona discharge passage, the electron-attached PM in the exhaust swirling in the exhaust swirling passage is unevenly distributed near the outer circumference wall of the exhaust swirling passage by electrostatic force and centrifugal force, and the EGR gas containing the electron-attached PM unevenly distributed is caused to flow into an exhaust swirling passage end part in a divided manner, and a discharged gas entry port is provided at the center cylinder serving as the negative electrode of the first corona discharge passage, an interior of the center cylinder serves as a discharged gas lead-out passage, and the discharged gas near the center cylinder in the exhaust swirling passage is caused to flow from the discharged gas entry port into the discharged gas lead-out passage in a divided manner, characterised in that a downstream side center cylinder concentric with the center cylinder is provided on a downstream side of the center cylinder in a discharged gas lead-out direction, an interior of this downstream side center cylinder serves as the second corona discharge passage, the downstream side center cylinder serves as a positive electrode of the second corona discharge passage, a core material inserted into a center part of the downstream side center cylinder serves as a negative electrode of the second corona discharge passage, a relay cylinder serving as an electric insulator is interposed between the center cylinder and the downstream side center cylinder, an interior of the relay cylinder serves as a discharged gas relay passage, the discharged gas lead-out passage and the second corona discharge passage are communicated with each other via the discharged gas relay passage, the core material is electrically connected with the center cylinder, and an outside of the downstream side center cylinder serves as a swirling approach passage positioned on an exhaust upstream side of the exhaust swirling passage.