ENGINE

It is an object of the invention to provide an engine, which can be decreased in height while the strength of a cylinder head is ensured. An engine 11 according to the invention is constructed such that a cam chain 19 is trained around a sprocket 17 fixed to a camshaft 16, a roof wall 13c of an accommodation chamber 13b, which accommodates therein the sprocket 17, is formed integral with a cylinder head 13, an opening 13h is formed on an upper surface of the cylinder head 13 to be adjacent to the roof wall 13c, and intake and exhaust valves 22, 23 face outside from the opening 13h, and that an opened surface of the opening 13h is positioned in a lower position than an upper end of the roof wall 13c and formed on the same plane.