An engine has an exhaust gas treatment apparatus attached thereto, wherein an exhaust pipe can be prevented from being damaged by a vibration of the engine body. An exhaust gas treatment apparatus is supported by an engine body and the engine body and the exhaust gas treatment apparatus communicate with each other through an exhaust pipe. The casing of the exhaust gas treatment apparatus consists of a plurality of casing units separable from each other. Connection flanges are disposed in respective end portions of the casing units. The casing units are coupled together by a connection of the connection flanges, and the exhaust gas treatment apparatus is supported by the engine body through the connection flanges.