Exhaust gas purification system

Provided is a technique whereby carbon monoxide generated as a by-product can be effectively utilized when carbon dioxide in exhaust gas of an internal combustion engine is subjected to a hydrogenation reaction and reused as fuel. An exhaust gas purification system (10) for an engine (1), which purifies exhaust gas discharged from the engine (1), is provided with: an exhaust gas purification device (4) which is provided in an exhaust pipe (16) of the engine (1) and which is provided with an exhaust gas purification catalyst having a NOx reduction function for reducing NOx in the exhaust gas; a carbon dioxide reduction device (11) having a carbon dioxide reduction catalyst for hydrogenating carbon dioxide contained in the exhaust gas that has passed through the exhaust gas purification device (4), reducing the carbon dioxide, and generating methanol; and a carbon monoxide supply device (12) that supplies the carbon monoxide, which is a by-product of the hydrogenation reaction, to the exhaust gas purification d