Fuel injection system for internal combustion engine

In an internal combustion engine in which fuel injection valves are arranged on the upstream side and on the downstream side of the throttle valve respectively, process values such as the engine speed and the vehicle speed will be restricted at upper limit values. An injection quantity restriction unit (1042) restricts fuel injection due to each of the fuel injection valves (8a,8b) when process values such as the vehicle speed and the engine speed reach or approach predetermined upper limit values. The injection quantity determination unit (105) determines the injection quantity (Qupper) of the upstream injection valve (8a) and the injection quantity (Qlower) of the downstream injection valve (8b).