VEHICLE AND SINGLE-CYLINDER FOUR-STROKE ENGINE UNIT

An object to provide a vehicle including a single-cylinder four-stroke engine unit with which the purification performance of purifying the exhaust gas by a catalyst is improved and the initial performance of a vehicle regarding the exhaust purification is maintained for a longer time, while the supporting structure is simplified. The upstream end of a single-combustion-chamber main catalyst 39 is provided upstream of the upstream end of a single-combustion-chamber silencer 35 in the flow direction of exhaust gas. The single-combustion-chamber main catalyst 39 purifies the exhaust gas exhausted from one combustion chamber 29 most in the exhaust path extending from the one combustion chamber 29 to a discharge port 35e. A single-combustion-chamber upstream oxygen detector 36 is provided upstream of the single-combustion-chamber main catalyst 39. A single-combustion-chamber downstream oxygen detector 37 is provided downstream of the single-combustion-chamber main catalyst 39.