A drive unit case (920) in this engine unit is provided with a crank shaft (60) disposed in the left-right direction of the vehicle, a drive shaft (73) and a second main shaft (72). A transmission shaft (79) is disposed parallel to the drive shaft (73) and transmits rotational power, which has been transmitted via a middle gear (76), to a propeller shaft (65). A second clutch (75), which transmits rotational power from the crank shaft (60) to the second main shaft (72), is connected freely detachably to an end (72a) of one side of the second main shaft (72) which protrudes from a drive unit case (920) more than the end of one side of the drive shaft (73), at a position that overlaps with at least one section of the middle gear (76) on the side of the shaft direction of the drive shaft (73).