A controller calculates a predicted value of the exhaust pressure between a catalyst and a filter for a case in which engine fuel containing no manganese is used continuously. Also, the controller calculates a correlation value proportional to the amount of heat received by the catalyst when the catalyst temperature is higher than or equal to the adhesion temperature of manganese oxide. Further, the controller determines that there is a removal requirement for removing manganese oxide from the catalyst when the difference between the predicted value and the detected pressure of the exhaust pressure between the catalyst and the filter is greater than a specified determination value, and the correlation value is greater than or equal to a specified determination value. The controller executes the removal process by performing fuel amount increase control when it is determined that there is a removal requirement.