1.  Field of the Invention
The invention relates to a power transmission system for a hydraulically driven working vehicle, especially, for a large-size vehicle. 
2.  Related Art
Conventionally, there is a well-known hydraulically driven working vehicle, equipped with a hydraulic pump disposed in a housing and drivingly connected to a prime mover (engine), and with a hydraulic motor disposed outside the housing and fluidly connected to the hydraulic pump so as to drive an axle.  U.S. Pat.  No.  6,732,828 discloses an example of this type of vehicle, wherein a hydraulic pump is disposed in a pump housing, a hydraulic motor for driving an axle is disposed in a transaxle housing separated from the pump housing, and a belt transmission system is interposed between a vertical output shaft of an upright engine and a working device. 
The upright arrangement of the prime mover (engine) with the vertical output shaft is available because the vehicle is small-sized, particularly, in the fore-and-aft direction.  If a working vehicle having such an arrangement of hydraulic pump and motor is large-sized, horizontal arrangement of a prime mover (engine) with a horizontal shaft is advantageous for ensuring a large space for other equipment including a working device (such as a midship mower) in the vertical direction.  However, the thing to be considered is layout of a power transmission system for drivingly connecting the prime mover to the hydraulic pump and the working device without hindering arrangement, attachment and detachment of the working device.