The purpose of the present invention is to provide a device for detecting a particulate substance in an internal combustion engine, which can estimate the amount of the discharged particulate substance with high accuracy. This device for detecting a particulate substance in an internal combustion engine comprises a sensor which is arranged in a passage for a discharged gas in the internal combustion engine and is equipped with a pair of electrodes for detecting the particulate substance in the discharged gas, a discharged amount estimation means for estimating the amount of the discharged particulate substance on the basis of an output from the sensor, and a parameter acquisition means for acquiring a predetermined parameter that serves as a measure for the ratio of the amount of the particulate substance accumulated in the sensor relative to the amount of the particulate substance in the discharged gas, wherein the discharged amount estimation means can correct an estimated value of the amount of the discharged particulate substance on the basis of the parameter acquired by the parameter acquisition means.