A breather device of an engine is connected to an engine suction system. A breather chamber thereof for separating a blowby gas generated inside a crank chamber of the engine into gas and liquid is formed so as to face to a mating face of a plurality of cases, including a crankcase, connected to each other via a gasket, and a communication port is formed to the gasket, through which the blowby gas comes and goes in a space within the plurality of cases to thereby carry out the gas-liquid separation of the blowby gas. A cam chamber receiving a cam for driving a valve train provided for a cylinder head of the engine is arranged at a connection portion of the plurality cases including the crankcase in a sectioned manner in adjacent to the crank chamber in an axial direction of the crankshaft, and the breather chamber is formed above the cam chamber, the breather chamber being provided with a main opening so as to face to the cam chamber.