An accumulation type fuel injection system (1) of a diesel engine (2) calculates a dimensionless interval (I 0 ) by dividing an injection interval (I) between a pilot injection and a main injection by a cycle (T) of pressure pulsation in an injection correcting operation for correcting the main injection. The fuel injection system (1) calculates correcting values corresponding to the dimensionless interval (I 0 ) from correction maps and calculates final main injection quantity (Q M ') and timing (t M ') by adding the correcting values (C Q , C t ) to main injection quantity (Q M ) and timing (t M ) calculated based on operating conditions of the engine (2).