A concentration of HC in an exhaust gas is estimated with a high degree of accuracy by making use of a particulate matter processing apparatus (1). In the particulate matter processing apparatus (1) in which a processing part (3) with an electrode (5) installed therein is arranged in an exhaust passage (2) of an internal combustion engine, wherein particulate matter is caused to aggregate by generating a potential difference between the electrode (5) and the processing part (3), provision is made for a power supply (6) that is connected to the electrode (5) and applies a voltage thereto, an insulation part (4) that insulates electricity between the processing part (3) and the exhaust passage (2), and a ground part (53) that grounds the processing part (3), a detection device (9) that detects an electric current in the ground part (53), and an estimation device (7) that estimates a concentration of HC in an exhaust gas based on the electric current detected by the detection device (9) at the time when the voltage is applied to the electrode (5) by means of the power supply (6).