An engine case houses engines in the inside of the case and is provided with a propulsion unit outside the case. A case main body housing the engines and assemblies of peripheral parts of the engines, and a case cover covering an opening at an upper portion of the case main body are included. Mufflers are installed on an exterior of a lower surface of the case, and on the lower surface of the case, housing portions housing the mufflers and exhaust hoses are formed.