Exhaust gas purifier

An exhaust gas purifier comprising:

• a first exhaust passage in which an exhaust gas of an engine mounted on a ship is configured to flow;
• a catalyst passage that is branched from the first exhaust passage and is configured to selectively reduce a nitrogen oxide included in the exhaust gas;
• a bypass passage that is branched from the first exhaust passage and bypasses the catalyst passage;
• a second exhaust passage in which the catalyst passage and the bypass passage are joined at an exhaust downstream side;
• a casing in which at least a part of the catalyst passage and at least a part of the bypass passage are formed;
• a selective catalytic reduction (SCR) catalyst that is disposed in the catalyst passage and is configured to selectively reduce a nitrogen oxide included in an exhaust gas flowing in the catalyst passage;
• and
• a backflow prevention section configured to prevent or reduce a backflow of an exhaust gas from the second exhaust passage to the catalyst passage, the backflow prevention section including:
• a first backflow prevention section positioned between the catalyst passage and the bypass passage;
• and
• a second backflow prevention section positioned between the SCR catalyst and the first backflow prevention section.