In this control device for an internal combustion engine (2), the internal combustion engine (2) is provided with an SCR system (8) arranged on an exhaust route (4), and a microparticle sensor (14) arranged downstream of the SCR system (8). The control device applies a microparticle-collecting voltage to the microparticle sensor (14) and acquires the output of the microparticle sensor (14) at a first timing following the start of application of the microparticle-collecting voltage. A predetermined control is executed in accordance with the output. The control device discontinues the predetermined control when a second timing is earlier than the first timing, the second timing being when the cumulative operation time of the internal combustion engine in a predetermined operation state where urea-related matter discharged downstream of the SCR system (8) increases, after the start of application of the microparticle-collecting voltage, arrives at a criterion time.