According to the present invention, there is disposed in an exhaust passage of an internal combustion engine a filter that traps particulate matter In an exhaust gas, and a catalyst with a three-way function is carried on the filter. At the filter regeneration, by controlling such as an injection amount of post injection, an air-fuel ratio of the exhaust gas at an outlet of the filter is controlled to a stoichiometric ratio, and also by controlling such as an intake air throttle valve, an oxygen concentration of the exhaust gas at an inlet of the filter is controlled. Hence, at the filter regeneration, the particulate can be reliably burned and removed, and at the same time, NOx in addition to HC and CO can be purified.