An exhaust gas purification device capable of enhancing handling operability such as maintenance of an engine includes two gas purification bodies which purify exhaust gas discharged from the engine, inner cases in which the gas purification bodies are incorporated, and outer cases in which the inner cases are incorporated. The outer cases are arranged side by side in a moving direction of exhaust gas and connected to each other. One of the adjoining inner cases is inserted into the other inner case to form a double-layer structure. A loosely-fitting gap is formed between an inner side surface of the one inner case and an outer side surface of the other inner case.