A straddled vehicle comprising: a single-cylinder four-stroke engine unit; a vehicle body frame supporting the single-cylinder four-stroke engine unit; and at least one vehicle component (86, 87) which is provided at least partially above the single-cylinder four-stroke engine unit, the single-cylinder four-stroke engine unit including: an engine main body including a horizontal cylinder member in which one combustion chamber which is partially formed by an inner surface of a cylinder hole and a single-combustion-chamber cylinder exhaust passage member in which exhaust gas exhausted from the one combustion chamber flows are formed, the horizontal cylinder member being provided so that a central axis of the cylinder hole (Cy) extends in a front-rear direction of the straddled vehicle, the engine main body being swingably supported by the vehicle body frame by a swing supporter, and the engine main body being provided below the at least one vehicle component; a single-combustion-chamber exhaust pipe connected to a downstream end of the single-combustion-chamber cylinder exhaust passage member of the engine main body; a single-combustion-chamber silencer including a discharge port exposed to the atmosphere, the silencer being connected to the single-combustion-chamber exhaust pipe to allow the exhaust gas to flow from a downstream end of the single-combustion-chamber exhaust pipe to the discharge port, and the silencer being configured to reduce sound generated by the exhaust gas; and a single-combustion-chamber main catalyst provided in the single-combustion-chamber exhaust pipe, the length of the single-combustion-chamber main catalyst in a flow direction of the exhaust gas being longer than the maximum width of the single-combustion-chamber main catalyst in a direction orthogonal to the flow direction, the single-combustion-chamber main catalyst being provided at least partially to the right of a right end of the swing supporter or the left of a left end of the swing supporter in a left-right direction of the straddled vehicle, the single-combustion-chamber main catalyst being at least partially provided on the outer side of the engine main body when the straddled vehicle is viewed in an up-down direction, and the single-combustion-chamber main catalyst purifying the exhaust gas exhausted from the one combustion chamber most in an exhaust path from the one combustion chamber to the discharge port. an engine main body including a horizontal cylinder member in which one combustion chamber which is partially formed by an inner surface of a cylinder hole and a single-combustion-chamber cylinder exhaust passage member in which exhaust gas exhausted from the one combustion chamber flows are formed, the horizontal cylinder member being provided so that a central axis of the cylinder hole (Cy) extends in a front-rear direction of the straddled vehicle, the engine main body being swingably supported by the vehicle body frame by a swing supporter, and the engine main body being provided below the at least one vehicle component; a single-combustion-chamber exhaust pipe connected to a downstream end of the single-combustion-chamber cylinder exhaust passage member of the engine main body; a single-combustion-chamber silencer including a discharge port exposed to the atmosphere, the silencer being connected to the single-combustion-chamber exhaust pipe to allow the exhaust gas to flow from a downstream end of the single-combustion-chamber exhaust pipe to the discharge port, and the silencer being configured to reduce sound generated by the exhaust gas; and a single-combustion-chamber main catalyst provided in the single-combustion-chamber exhaust pipe, the length of the single-combustion-chamber main catalyst in a flow direction of the exhaust gas being longer than the maximum width of the single-combustion-chamber main catalyst in a direction orthogonal to the flow direction, the single-combustion-chamber main catalyst being provided at least partially to the right of a right end of the swing supporter or the left of a left end of the swing supporter in a left-right direction of the straddled vehicle, the single-combustion-chamber main catalyst being at least partially provided on the outer side of the engine main body when the straddled vehicle is viewed in an up-down direction, and the single-combustion-chamber main catalyst purifying the exhaust gas exhausted from the one combustion chamber most in an exhaust path from the one combustion chamber to the discharge port.