In the present studies, a new accumulation-type fuel injection system was developed to control the injection pressure independently of engine speed. The injection characteristics and the effects of the system on combustion characteristics represented by exhaust smoke density, specific fuel consumption and rate of heat release, in a small-sized direct-injection type diesel engine were investigated and the following was made clear : (1) Making use of the new injection system, exhaust smoke density was fairly decreased even at low engine speeds. (2) It was effective on the improvement of combustion characteristics to use the injection nozzle with smaller hole diameter corresponding to higher injection pressure, because of the increase in excess air ratio of fuel spray. (3) Increase of injection pressure made combustion characteristics insensitive to swirl intensity and improved specific fuel consumption, especially at retarded injection timing. (4)The shape of injection rate versus crank angle is important to reduce exhaust smoke density without a serious increase in maximum combustion pressure.