In an injector having three concentrated fuel spray bands, one of the fuel spray bands is directed to an spark plug, and the others are directed to curved grooves on a piston. The sprays that enter each groove advance along each groove, mutually collide substantially under the spark plug, and are ascended. Further, these spray bands are carried to the vicinity of the spark plug by a tumble flow and stable stratified air-fuel mixture is formed. As described above, stable and satisfactory stratified combustion can be made.