Abstract: A gear case assembly includes an upper gear case and a lower gear case accommodating a drive axle, at least one rotation axle receiving power from the drive axle, and a power transmission unit for transmitting the power to the at least one rotation axis. The upper and lower gear cases are horizontally divided, and upper and a lower shrouds are integrally formed on the upper and lower gear cases proximate to ends of the rotation axis. The upper and lower shrouds form a surface for guiding a fluid that flows from an impeller connected to the rotation axle, and are horizontally divided. Scroll cases mounted on the upper and lower gear cases, together with the upper and lower shrouds, define a path for guiding the fluid that flows from the impeller. A common plane divides the upper and lower gear cases, and also divides the upper and lower shrouds.