An engine including a chain room, comprising: a crankshaft; a camshaft; a first sprocket attached to the crankshaft; a second sprocket attached to the camshaft; a crankcase containing the first sprocket; a cylinder body attached to the crankcase; a cylinder head attached to the cylinder body and containing the second sprocket; a chain wound around the first sprocket and the second sprocket; and a tensioning member configured to tension the chain, wherein the tensioning member includes: a leaf spring; and a contact member supporting the leaf spring and contactable with the chain in the chain room, the crankcase, the cylinder body and the cylinder head form the chain room including a first subroom, a second subroom and a third subroom containing the chain, the first subroom is visible through an opening in the crankcase, the engine further includes: a support shaft inserted into a support hole formed in the tensioning member for swingably supporting the tensioning member; and a support member contactable with a supported portion of the tensioning member to support the tensioning member, and the support member is configured to support the tensioning member in such a way that the supported portion is slidable, characterized in that the cylinder body includes a cylindrical portion forming second subroom as a part of the chain room, the support shaft is swingably supporting the tensioning member on the cylinder head, and the support member is provided in the crankcase. a crankshaft; a camshaft; a first sprocket attached to the crankshaft; a second sprocket attached to the camshaft; a crankcase containing the first sprocket; a cylinder body attached to the crankcase; a cylinder head attached to the cylinder body and containing the second sprocket; a chain wound around the first sprocket and the second sprocket; and a tensioning member configured to tension the chain, wherein the tensioning member includes: a leaf spring; and a contact member supporting the leaf spring and contactable with the chain in the chain room, the crankcase, the cylinder body and the cylinder head form the chain room including a first subroom, a second subroom and a third subroom containing the chain, the first subroom is visible through an opening in the crankcase, a leaf spring; and a contact member supporting the leaf spring and contactable with the chain in the chain room, the crankcase, the cylinder body and the cylinder head form the chain room including a first subroom, a second subroom and a third subroom containing the chain, the first subroom is visible through an opening in the crankcase, the engine further includes: a support shaft inserted into a support hole formed in the tensioning member for swingably supporting the tensioning member; and a support member contactable with a supported portion of the tensioning member to support the tensioning member, and the support member is configured to support the tensioning member in such a way that the supported portion is slidable, characterized in that the cylinder body includes a cylindrical portion forming second subroom as a part of the chain room, the support shaft is swingably supporting the tensioning member on the cylinder head, and the support member is provided in the crankcase. a support shaft inserted into a support hole formed in the tensioning member for swingably supporting the tensioning member; and a support member contactable with a supported portion of the tensioning member to support the tensioning member, and the support member is configured to support the tensioning member in such a way that the supported portion is slidable, characterized in that the cylinder body includes a cylindrical portion forming second subroom as a part of the chain room, the support shaft is swingably supporting the tensioning member on the cylinder head, and the support member is provided in the crankcase.