A control device of an internal combustion engine, the internal combustion engine including a fuel injection device that injects fuel into a cylinder, comprising: an electronic control unit configured to: control the fuel injection device so as to perform post injection comprising multistage post injections, on an expansion stroke of the internal combustion engine after combustion caused by main injection; and control the fuel injection device such that an injection amount of an earliest-stage post injection as one of the multistage post injections is smaller than the injection amount of each of subsequent-stage post injections that follow the earliest-stage post injection, characterized in that, the electronic control unit is configured to control the fuel injection device, so as to perform at least three-stage post injections comprising the earliest-stage post injection, a last-stage post injection, and a middle-stage post injection between the earliest-stage post injection and the last-stage post injection; the electronic control unit is configured to set a target injection amount based on which the injection amounts of the middle-stage post injection and the last-stage post injection are increased according to an acceleration request, when the acceleration request is generated to the internal combustion engine; and the electronic control unit is configured to control the fuel injection device so as to increase the injection amount of the middle-stage post injection before increasing the injection amount of the last-stage post injection, according to operating conditions of the internal combustion engine, when the acceleration request is generated to the internal combustion engine, and increase the injection amount of the last-stage post injection, after the injection amount of the middle-stage post injection is increased to a target value of the middle-stage post injection which is determined according to the target injection amount. control the fuel injection device so as to perform post injection comprising multistage post injections, on an expansion stroke of the internal combustion engine after combustion caused by main injection; and control the fuel injection device such that an injection amount of an earliest-stage post injection as one of the multistage post injections is smaller than the injection amount of each of subsequent-stage post injections that follow the earliest-stage post injection, characterized in that, the electronic control unit is configured to control the fuel injection device, so as to perform at least three-stage post injections comprising the earliest-stage post injection, a last-stage post injection, and a middle-stage post injection between the earliest-stage post injection and the last-stage post injection; the electronic control unit is configured to set a target injection amount based on which the injection amounts of the middle-stage post injection and the last-stage post injection are increased according to an acceleration request, when the acceleration request is generated to the internal combustion engine; and the electronic control unit is configured to control the fuel injection device so as to increase the injection amount of the middle-stage post injection before increasing the injection amount of the last-stage post injection, according to operating conditions of the internal combustion engine, when the acceleration request is generated to the internal combustion engine, and increase the injection amount of the last-stage post injection, after the injection amount of the middle-stage post injection is increased to a target value of the middle-stage post injection which is determined according to the target injection amount.