An exhaust gas purifying device for a diesel engine comprising an outer casing accommodating a catalyst-carrying honeycomb having a dustfree structure, and a baffle plate arranged in the outer casing of the device between an gas inlet of the case and the catalyst-carrying honeycomb. The honeycomb structure has open cells having a size equal to or less than 100 cells per square inch, to allow particles to pass therethrough. The baffle plate directs the exhaust gas over surface of the catalyst-carrying honeycomb, with a uniform distribution thereof.