A cross recess is provided at a fastening seat portion of a cylinder head in which exhaust port outlets are arranged in two rows and two in each row. A cross protrusion that is fittable to the cross recess is provided at a flange of an exhaust manifold. A gasket has a cross opening through which the cross protrusion is insertable. The exhaust manifold is fastened to the cylinder head by passing the cross protrusion of the flange of the exhaust manifold through the cross opening of the gasket and then fitting the cross protrusion to the cross recess of the fastening seat portion of the cylinder head.