1. A fuel injection system including a control unit, which performs a learning injection based on a learning injection quantity and obtains multiple influence values of an operating state of an engine generated through the learning injection in order to calculate a learning value for correcting the injection quantity in a normal operation based on the obtained multiple influence values, wherein the control unit includes determining means for determining whether the influence value obtained during the learning injection is within a predetermined range of the influence value set in accordance with a characteristic value of the operating state of the engine, and the control unit calculates a provisional learning injection quantity for bringing subsequent influence values into the predetermined range when the influence value obtained in an early stage of the obtainment of the influence values is out of the predetermined range, and calculates the other influence values by performing the other learning injections based on the provisional learning injection quantity.