An amount of aggregation of particulate matter is estimated with a high degree of accuracy. A particulate matter processing apparatus in which a processing part with an electrode installed therein is arranged in an exhaust passage of an internal combustion engine, wherein particulate matter is caused to aggregate by generating a potential difference between the electrode and the processing part, is provided with a power supply that is connected to the electrode and applies a voltage thereto, a current detection device that detects an electric current which passes through the electrode, an estimation device that estimates an amount of aggregation of the particulate matter based on the electric current detected at the time when the voltage is applied to the electrode, an air fuel ratio detection device that detects or estimates an air fuel ratio of an exhaust gas which flows through the exhaust passage, and a prohibition device which prohibits an estimation by the estimation device in the case of a rich air fuel ratio.