Outboard motor

An outboard motor comprising:

• a first catalyst, which is installed in an exhaust flow passage of an engine;
• a second catalyst, which is installed on a downstream side of the first catalyst;
• exhaust gas sensors, which are installed on an upstream side and a downstream side of the first catalyst;
• and
• a controller, which performs combustion control in the engine, wherein
• based on a value being detected by the exhaust gas sensor, which is installed on the downstream side, the controller calculates a purification rate of exhaust gas after passing through the first catalyst and based on the purification rate of the exhaust gas after passing through the first catalyst, determines what amount of purification attained by the second catalyst makes exhaust gas after passing through the second catalyst appropriate, and
• the controller calculates the purification rate of exhaust gas based on the value being detected by the exhaust gas sensor, which is installed on the downstream side and performs the combustion control in the engine so as to make the purification rate of the exhaust gas appropriate.