To provide a fuel supply system of a cylinder direct injection CNG engine capable of extending a cruising distance by the effective use of CNG fuel by simple structure and control and withdrawing fuel economy merit by establishing stratified combustion up to a high-load/high rotation zone.

This fuel supply system of an CNG engine 10 comprises a CNG fuel cylinder 12, a delivery pipe 13, an injector 17, and a fuel supply pipe 14 connecting the cylinder 12 to the delivery pipe 13. A regulator 15 reducing fuel pressure to approximately the atmospheric pressure and a variable boosting pump 16 boosting fuel pressure-reduced by the regulator 15 are installed in the fuel supply pipe 14. The fuel is boosted to a specified injection pressure by the variable boosting pump 16 based on the operating conditions of the CNG engine 10.

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