PURPOSE: To provide a small-sized lightweight device for treating exhaust gas in which exhaust gas can be treated by irradiation with electron beams having the irreducible min. of energy without requiring high energy electron beams.

CONSTITUTION: In this device for treating exhaust gas, harmful components in exhaust gas are allowed to react by irradiating the exhaust gas with electron beams from an electron beam radiator and the components are removed as harmless components. The electron beam radiator is a device for irradiating a substance (photoelectron emitting plate 18) set in an exhaust gas duct 11 through which exhaust gas flows with electromagnetic waves (UV light source 15) having short wavelength and directly irradiating the exhaust gas with photoelectrons 17 emitted from the substance.