An axle driving unit includes a pair of axles, a differential unit for differently connecting the pair of axles to each other, a hydraulic pump, a hydraulic motor, a motor shaft, an output gear on said motor shaft for drivingly connecting to said differential unit, a center section having a pump mounting surface and a motor mounting surface onto which said hydraulic pump and the hydraulic motor are mounted respectively, a housing constituted by a first housing part and a second housing part joined to each other at a joint surface, and a fastener fastening the center section to the first housing part. The center section is entirely disposed in the first housing part, whereby the hydraulic pump, the hydraulic motor and the output gear are entirely contained in the first housing part. The motor mounting surface may be disposed in parallel to the joint surface of the housing. The hydraulic pump may be located a distance from said pair of axles that is greater than a distance from the hydraulic motor to the pair of axles.