A fuel supply system supplies composite fuel containing alcohol and gasoline to multiple cylinders of an internal combustion engine. The composite fuel includes main-fuel and sub-fuel. The sub-fuel is lower than main-fuel in concentration of alcohol. Each of multiple first fuel injection valves is provided to each of the cylinders for injecting fuel. Each of multiple second fuel injection valves is provided to each of the cylinders for injecting fuel. A fuel inlet portion supplies at least sub-fuel to each of the first fuel injection valves and each of the second fuel injection valves. A selector control unit selects one of main-fuel and sub-fuel supplied through the fuel inlet portion to each of the first fuel injection valves.