STRADDLED VEHICLE ENGINE UNIT AND STRADDLED VEHICLE

Provided is a straddled vehicle engine unit and a straddled vehicle, capable of detecting a misfire in an internal combustion engine mounted to the straddled vehicle with high accuracy. The straddled vehicle engine unit includes: an internal combustion engine having a crankshaft and a crank angle signal output unit; and a misfire detection device. The misfire detection device includes: a crankshaft rotation speed fluctuation physical quantity acquisition unit that acquires a physical quantity related to the amount of fluctuation in the rotation speed of the crankshaft; and a misfire determination unit. The misfire determination unit determines that a misfire has occurred upon detecting both: lowering of the rotation speed of the crankshaft at a first preceding timing based on a differential between a first preceding physical quantity and a second preceding physical quantity, the first preceding timing corresponding to a specific kind of stroke before, the first preceding physical quantity being a physical quantity acquired at the first preceding timing, the second preceding physical quantity being a physical quantity acquired at a second preceding timing before the first preceding timing; and completion of the lowering of the rotation speed at an acquisition timing based on a differential between the crankshaft rotation speed fluctuation physical quantity and the first preceding physical quantity.