To protect an engine without stopping the engine when the detection of the running state of an engine is wrong and to give a user the information to the effect.

In this fuel injection control system of an outboard motor, throttle valves are provided independently in respective intake passages of plural cylinders, a first fuel injection mode 100 for controlling the injection amount by an intake negative pressure and number of rotation at the low opening side of this throttle valve is carried out, a second fuel injection mode 101 for controlling the injection amount by the throttle opening and number of rotation at the high opening side of the throttle valve is carried out and the fuel is injected by switching to the second fuel injection mode 101 independently at the wrong detection time of the intake negative pressure and the first fuel injection mode 100 independently at the wrong detection time of the throttle opening. At the switching time from the fuel injection of the common use of the first fuel injection mode 100 and the second fuel injection mode 101 to the independent fuel injection of the first fuel injection mode 100 or the second fuel injection mode 101, the warning for reducing the number of rotation of the engine is carried out.