A ship propulsion unit (10) includes: an engine (21) including a crankshaft (23) extending in a front-rear direction of a ship; a propeller shaft (51); a power transmission mechanism (60) configured to couple the crankshaft (23) and the propeller shaft (51); an upper case (30); and a lower case (40) accommodating the propeller shaft (51) and connected to the upper case (30). The power transmission mechanism (60) includes a drive shaft (65) extending from the upper case (30) toward the lower case (40). The upper case (30) and the engine (21) are fixed to a ship body (2). A connection portion between the upper case (30) and the lower case (40) is provided with a rotation mechanism (70) configured to rotate the lower case (40) around an axis of the drive shaft (65).