To provide a fuel injection control device of an internal combustion engine capable of improving filling efficiency more than conventional filling efficiency, by further properly controlling the fuel injection timing of gas fuel.

Intake pressure peak periods TPK11 and TPK12 including the timing when intake pressure in the vicinity of a first fuel injection valve 21 takes a high pressure side peak value, are determined based on intake pressure PI detected by an intake pressure sensor 32 arranged in the vicinity of the first fuel injection valve 21, and fuel injection is executed in the intake pressure peak periods. In a high load or high rotation operation state of the engine, both the first and second fuel injection valves 21 and 22 are used, and the fuel injection is executed in the intake pressure peak periods TPK11 and TPK21 including the timing when the intake pressure in the vicinity of the respective fuel injection valves takes the high pressure side peak value.