in a multi - cylinder internal combustion engine with a single fuel injection valve provided in a manifold entrance , a fuel supply system including a primary and a secondary passage formed by partitioning the manifold entrance is disclosed wherein the portion of the secondary passage located on the outer circumferential surface of the primary passage in the joined portion of each exit of both passages is formed ring - shaped and the exits face the floor surface of a riser portion . thus , the fuel supply system makes it possible to maintain satisfactory fuel atomizing characteristics during all driving conditions and to obtain uniform mixture distribution characteristics with respect to each engine cylinder .