Aggregation of particulate matter is facilitated. Provision is made for an electrode that is arranged in an exhaust passage of an internal combustion engine with a voltage to be applied thereto being able to be changed, a detection device that detects an electric current passing through the electrode, a determination device that determines whether a pulse current has been generated in the electric current detected by the detection device, and a control device that reduces the voltage to be applied more than that at this time in cases where a determination has been made by the determination device that a pulse current has been generated.