A fuel injection system for internal combustion engines, having a fuel injector that can be acted upon by a high-pressure fuel source includes a pressure booster, which contains a movable boosting element dividing a work chamber which can be made to communicate with the high-pressure source via a high-pressure line from a high-pressure chamber that acts on the fuel injector. The high-pressure from chamber is variable by filling and evacuating a differential pressure chamber of the pressure booster. A filter element is received in a line portion that branches off from the high-pressure line and is upstream of flow connections for filling the differential and high pressure chambers.