A vessel propulsion apparatus, comprising: a first shaft that is rotationally driven; a drive gear connected to the first shaft; a tubular first driven gear that engages the drive gear; a tubular second driven gear that engages the drive gear; a dog clutch that is switchable by a shift operation between a connected state in which the dog clutch is connected to one of the first driven gear and the second driven gear and a non-connected state in which the dog clutch is not connected to either of the first driven gear and the second driven gear; a second shaft that is inserted in the first driven gear and in the second driven gear, that is connected to the dog clutch, and that is arranged to undergo a thrust; a first bearing disposed between the first driven gear and the second shaft; a second bearing disposed between the second driven gear and the second shaft; a case that contains the drive gear, the first driven gear, the second driven gear, the dog clutch, the first bearing, and the second bearing; characterised in that a thrust applied to the second shaft is transmitted to the case via the first bearing and the first driven gear or via the second bearing and the second driven gear; and in that it comprises an adjusting member that is arranged to press the first driven gear in a first direction along an axis of the second shaft and to press the second driven gear in a second direction along the axis of the second shaft, the second direction being opposite to the first direction, that is disposed between the second shaft and at least one of the first driven gear and the second driven gear, and that is arranged to apply a preload onto the first bearing and the second bearing. a first shaft that is rotationally driven; a drive gear connected to the first shaft; a tubular first driven gear that engages the drive gear; a tubular second driven gear that engages the drive gear; a dog clutch that is switchable by a shift operation between a connected state in which the dog clutch is connected to one of the first driven gear and the second driven gear and a non-connected state in which the dog clutch is not connected to either of the first driven gear and the second driven gear; a second shaft that is inserted in the first driven gear and in the second driven gear, that is connected to the dog clutch, and that is arranged to undergo a thrust; a first bearing disposed between the first driven gear and the second shaft; a second bearing disposed between the second driven gear and the second shaft; a case that contains the drive gear, the first driven gear, the second driven gear, the dog clutch, the first bearing, and the second bearing; characterised in that a thrust applied to the second shaft is transmitted to the case via the first bearing and the first driven gear or via the second bearing and the second driven gear; and in that it comprises an adjusting member that is arranged to press the first driven gear in a first direction along an axis of the second shaft and to press the second driven gear in a second direction along the axis of the second shaft, the second direction being opposite to the first direction, that is disposed between the second shaft and at least one of the first driven gear and the second driven gear, and that is arranged to apply a preload onto the first bearing and the second bearing. an adjusting member that is arranged to press the first driven gear in a first direction along an axis of the second shaft and to press the second driven gear in a second direction along the axis of the second shaft, the second direction being opposite to the first direction, that is disposed between the second shaft and at least one of the first driven gear and the second driven gear, and that is arranged to apply a preload onto the first bearing and the second bearing.