The problem is to regenerate the purification ability of an exhaust gas purification device more reliably or efficiently in an exhaust gas purification system that combines a plurality of branch passages branch off from an exhaust gas passage and exhaust gas purification devices. When the purification ability of an exhaust gas purification device is regenerated, in the branch passage where the exhaust gas purification device is provided whose purification ability is to be regenerated, the opening angle of an exhaust gas flow volume control valve is set to the minimum opening angle that can reliably transport a reducing agent that is added from a reducing agent addition section. While the opening angle is maintained, the reducing agent is added. After the addition of the reducing agent is complete, the opening angle of an exhaust gas flow volume control valve is closed completely.