A wall flow type particulate filter (24) is arranged inside the exhaust passage of an internal combustion engine where combustion is performed under an excess of oxygen. The particulate filter carries a solid acid. The solid acid has an acid strength which is higher than the acid strength of sulfurous acid and lower than the acid strength of sulfuric acid. To remove the ash from the particulate filter, ash atomization processing for rendering the state of the particulate filter a state where the exhaust gas which flows into the particulate filter is lowered in concentration of oxygen and the particulate filter is raised in temperature is temporarily performed.