A controller of a common rail fuel injection system that accumulates high-pressure fuel in a common rail and supplies the accumulated fuel to an engine through a fuel injection valve, the controller performing multiple injection control for injecting the fuel multiple times during one combustion cycle of the engine with the use of one fuel injection valve, the controller comprising: an estimating means (M1, M2, S203) for estimating an actual fuel injection amount injected from the fuel injection valve; a calculating means (M3, S206) for calculating a control deviation time (ΔT) of an interval time between adjacent injections of the multiple injection based on a difference between the actual fuel injection amount estimated by the estimating means (M1, M2, S203) and a present injection amount command value; and a correcting means (S108, S207, S208, S304) for correcting a control parameter of the fuel injection control using the fuel injection valve based on the control deviation time (ΔT) of the interval time calculated by the calculating means, wherein the calculating means (M3, S206) includes: a first means for changing the interval time by a predetermined time; and a second means for calculating an injection amount deviation (ΔQ) as a difference between the fuel injection amount estimated by the estimating means when the interval time is changed and the injection amount command value and for calculating the control deviation time (ΔT) of the interval time based on a correlation between a changed time of the interval time and the injection amount deviation (ΔQ), wherein the correlation between the changed time of the interval time and the injection amount deviation (ΔQ) is obtained in a predetermined standard state, the standard state being a state in which there is no deviation in the interval time at the time when the control parameter of the fuel injection control is adjusted, and the calculating means (M3, S206) calculates the control deviation time based on the correlation as of the calculation and the correlation in the standard state, characterized in that the correlation is defined in advance for each one of multiple interval times providing the same fuel pressure in the common rail as of a start of a latter injection out of the two adjacent injections, and the calculating means (M3, S206) calculates the control deviation time (ΔT) based on the correlation corresponding to the actual interval time and the defined correlations corresponding to the multiple interval times. an estimating means (M1, M2, S203) for estimating an actual fuel injection amount injected from the fuel injection valve; a calculating means (M3, S206) for calculating a control deviation time (ΔT) of an interval time between adjacent injections of the multiple injection based on a difference between the actual fuel injection amount estimated by the estimating means (M1, M2, S203) and a present injection amount command value; and a correcting means (S108, S207, S208, S304) for correcting a control parameter of the fuel injection control using the fuel injection valve based on the control deviation time (ΔT) of the interval time calculated by the calculating means, wherein the calculating means (M3, S206) includes: a first means for changing the interval time by a predetermined time; and a second means for calculating an injection amount deviation (ΔQ) as a difference between the fuel injection amount estimated by the estimating means when the interval time is changed and the injection amount command value and for calculating the control deviation time (ΔT) of the interval time based on a correlation between a changed time of the interval time and the injection amount deviation (ΔQ), wherein a first means for changing the interval time by a predetermined time; and a second means for calculating an injection amount deviation (ΔQ) as a difference between the fuel injection amount estimated by the estimating means when the interval time is changed and the injection amount command value and for calculating the control deviation time (ΔT) of the interval time based on a correlation between a changed time of the interval time and the injection amount deviation (ΔQ), wherein the correlation between the changed time of the interval time and the injection amount deviation (ΔQ) is obtained in a predetermined standard state, the standard state being a state in which there is no deviation in the interval time at the time when the control parameter of the fuel injection control is adjusted, and the calculating means (M3, S206) calculates the control deviation time based on the correlation as of the calculation and the correlation in the standard state, characterized in that the correlation is defined in advance for each one of multiple interval times providing the same fuel pressure in the common rail as of a start of a latter injection out of the two adjacent injections, and the calculating means (M3, S206) calculates the control deviation time (ΔT) based on the correlation corresponding to the actual interval time and the defined correlations corresponding to the multiple interval times.