A control device for an internal combustion engine, the internal combustion engine comprising: an engine body; an exhaust after-treatment system installed in an exhaust passage of the engine body; a first exhaust temperature sensor provided in the exhaust passage at an upstream side from the exhaust after-treatment system in an exhaust flow direction; and a second exhaust temperature sensor provided in the exhaust passage at a downstream side from the exhaust after-treatment system in the exhaust flow direction, wherein the control device comprises: a first exhaust temperature calculation part configured to calculate a temperature of exhaust flowing into the exhaust after-treatment system as a first exhaust temperature, based on a detection value of the first exhaust temperature sensor; a second exhaust temperature calculation part configured to calculate a temperature of exhaust flowing out from the exhaust after-treatment system as a second exhaust temperature, based on a detection value of the second exhaust temperature sensor; a rate of change over time calculation part configured to calculate a rate of change over time of the first exhaust temperature and a rate of change over time of the second exhaust temperature; and a judgment part configured to judge if the exhaust after-treatment system is in a removed state removed from the exhaust passage based on a difference between the rate of change over time of the first exhaust temperature and the rate of change over time of the second exhaust temperature, when a predetermined condition stands, characterized in that as the predetermined condition, the rate of change over time of the first exhaust temperature is being a predetermined rate of change or less is included, and the predetermined rate of change is a negative value. the internal combustion engine comprising: an engine body; an exhaust after-treatment system installed in an exhaust passage of the engine body; an engine body; an exhaust after-treatment system installed in an exhaust passage of the engine body; a first exhaust temperature sensor provided in the exhaust passage at an upstream side from the exhaust after-treatment system in an exhaust flow direction; and a second exhaust temperature sensor provided in the exhaust passage at a downstream side from the exhaust after-treatment system in the exhaust flow direction, wherein the control device comprises: a first exhaust temperature calculation part configured to calculate a temperature of exhaust flowing into the exhaust after-treatment system as a first exhaust temperature, based on a detection value of the first exhaust temperature sensor; a second exhaust temperature calculation part configured to calculate a temperature of exhaust flowing out from the exhaust after-treatment system as a second exhaust temperature, based on a detection value of the second exhaust temperature sensor; a rate of change over time calculation part configured to calculate a rate of change over time of the first exhaust temperature and a rate of change over time of the second exhaust temperature; and a judgment part configured to judge if the exhaust after-treatment system is in a removed state removed from the exhaust passage based on a difference between the rate of change over time of the first exhaust temperature and the rate of change over time of the second exhaust temperature, a first exhaust temperature calculation part configured to calculate a temperature of exhaust flowing into the exhaust after-treatment system as a first exhaust temperature, based on a detection value of the first exhaust temperature sensor; a second exhaust temperature calculation part configured to calculate a temperature of exhaust flowing out from the exhaust after-treatment system as a second exhaust temperature, based on a detection value of the second exhaust temperature sensor; a rate of change over time calculation part configured to calculate a rate of change over time of the first exhaust temperature and a rate of change over time of the second exhaust temperature; and a judgment part configured to judge if the exhaust after-treatment system is in a removed state removed from the exhaust passage based on a difference between the rate of change over time of the first exhaust temperature and the rate of change over time of the second exhaust temperature, as the predetermined condition, the rate of change over time of the first exhaust temperature is being a predetermined rate of change or less is included, and the predetermined rate of change is a negative value.