There is provided a control device that controls an injection amount of a reducing agent to be supplied to a selective reduction catalyst provided in an exhaust passage of an internal combustion engine. The control device includes a pre-correction injection amount calculation unit configured to calculate a pre-correction injection amount of the reducing agent based on an operating state of the engine, and an injection amount correction unit configured to calculate a corrected injection amount obtained by correcting the pre-correction injection amount, based on a rate of change over time of a rotation speed of the engine and a rate of change over time of a fuel injection amount of the engine, such that the injection amount of the reducing agent increases when at least both the rate of change over time of the rotation speed and the rate of change over time of the fuel injection amount are positive.