To provide a fuel injection adjusting apparatus and a injection adjusting method thereof that can inexpensively, simply, and quickly adjust fuel injection amounts Mp, Mm of respective pilot injection and main injection and an pilot interval Tp by fuel injection amount measurement.

For adjusting the pilot interval Tp, a single injection completion timing with respect to a predetermined single fuel injection amount Mt, which is obtained from an elongation of a characteristic curve Hc for obtaining the fuel injection amount Mp of the pilot injection, is grasped as a main injection completion timing T2. At the single injection completion timing, the timing of operating a solenoid valve is adjusted to increase or decrease the fuel injection amount Mm so that the fuel injection amount Mm for the main injection is set as a difference between a total fuel injection amount M and the fuel injection amount Mp of the pilot injection based on the characteristic curve Hc.