Control system for internal combustion engine

In an internal combustion engine equipped with an injector (11) for cylinder-inside injection to inject fuel into a cylinder (1a) and an injector (12) for intake port injection to inject fuel into an intake port (20), both the injectors (11; 12) being switched for use depending upon operating conditions, wherein when an operating condition range using either one of the first or the second injector (11; 12) is switched to an operating condition range using the other one (12; 11) thereof, the amount of fuel to be injected by the either one of the first or the second injector (11; 12) is gradually decreased and the amount of fuel to be injected by the other one (12; 11) is gradually increased over a predetermined period during the switching. Further, at the time of the switching, at least one of ignition timing and throttle opening angle is gradually varied.