a device for purifying exhaust gas of an internal combustion engine which provides improved purifying efficiency even in a lean operating condition without deteriorating the fuel efficiency . the device includes an electrochemical catalyst 5 installed in the exhaust system 3 of the internal combustion engine 1 , the electro chemical catalyst 5 containing an electron conducting substance and an ion conducting substance , the oxidizing reaction and the reducing reaction being promoted by the conduction of ions and electrons , thereby to electrochemically purify the exhaust gas g in the exhaust system .