A fuel injection device of a common rail type fuel injection system for an engine, comprising: at least one fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f) disposed in a fuel passage between a point of a pipe connected to a fuel discharge port of a common rail apart from the common rail by a certain distance and a fuel injection hole of an injector connected to the pipe, the sensor (20a, 20b, 20c, 20d, 20e, 20f) measuring a fuel pressure at a position where the sensor (20a, 20b, 20c, 20d, 20e, 20f) is disposed; and a pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38) for sensing a pressure fluctuation caused by at least one of an injection operation of the injector and actual injection actually performed through the injection operation based on a sensor output from the fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f), wherein the pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38) detects a pressure drop point indicative of a predetermined pressure drop mode as the pressure fluctuation caused by at least one of the injection operation of the injector and the actual injection thereof in a predetermined period starting from predetermined timing near or after an injection start command to the injector based on the pressure value of each time measured by the fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f), the fuel injection device further comprising: a pressure drop detection type injection timing obtaining device (S35, S351, S37, S371) for determining timing at which the injection rate is the maximum based on pressure drop point detection timing of the pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38), characterized by an injection rate obtaining device for determining the injection rate at a time based on a difference amount between a reference pressure value and a pressure value measured at the time by the fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f), using the pressure value as of the detection of the pressure drop point by the pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38) as the reference pressure value. at least one fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f) disposed in a fuel passage between a point of a pipe connected to a fuel discharge port of a common rail apart from the common rail by a certain distance and a fuel injection hole of an injector connected to the pipe, the sensor (20a, 20b, 20c, 20d, 20e, 20f) measuring a fuel pressure at a position where the sensor (20a, 20b, 20c, 20d, 20e, 20f) is disposed; and a pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38) for sensing a pressure fluctuation caused by at least one of an injection operation of the injector and actual injection actually performed through the injection operation based on a sensor output from the fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f), wherein the pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38) detects a pressure drop point indicative of a predetermined pressure drop mode as the pressure fluctuation caused by at least one of the injection operation of the injector and the actual injection thereof in a predetermined period starting from predetermined timing near or after an injection start command to the injector based on the pressure value of each time measured by the fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f), the fuel injection device further comprising: a pressure drop detection type injection timing obtaining device (S35, S351, S37, S371) for determining timing at which the injection rate is the maximum based on pressure drop point detection timing of the pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38), characterized by an injection rate obtaining device for determining the injection rate at a time based on a difference amount between a reference pressure value and a pressure value measured at the time by the fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f), using the pressure value as of the detection of the pressure drop point by the pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38) as the reference pressure value. a pressure drop detection type injection timing obtaining device (S35, S351, S37, S371) for determining timing at which the injection rate is the maximum based on pressure drop point detection timing of the pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38), characterized by an injection rate obtaining device for determining the injection rate at a time based on a difference amount between a reference pressure value and a pressure value measured at the time by the fuel passage pressure sensor (20a, 20b, 20c, 20d, 20e, 20f), using the pressure value as of the detection of the pressure drop point by the pressure fluctuation sensing device (S31, S32, S331, S332, S34, S35, S36, S351, S361, S362, S37, S371, S38) as the reference pressure value.