In an apparatus, an actual fuel spray characteristic obtaining unit obtains, based on an operation of a learning fuel injection instructing unit in a learning mode, an actual fuel spray characteristic of an injector relative to a variable of a target interval period within at least one section in a usable range therefor. A phase difference calculating unit calculates a phase difference between a reference fuel spray characteristic and the obtained actual fuel spray characteristic. A phase correcting unit shifts the reference fuel spray characteristic by the calculated phase difference such that the reference fuel spray characteristic is corrected to approach the obtained actual fuel spray characteristic.