Abstract: A hydraulic transmission apparatus has: a swash plate hydraulic pump having a pump cylinder block; and a swash plate hydraulic motor which has a motor cylinder block and is arranged coaxially in a line with the swash plate pump so as to face in the same direction as the hydraulic pump. The hydraulic pump and motor area connected by a hydraulic passage system. The pump swash plate is provided at a side of the motor cylinder block, the side being close to the hydraulic pump. The motor swash plate is provided at a side of the motor cylinder block, the side being remote from the hydraulic pump, and its tilt angle is varied so as to vary the capacity of the hydraulic motor. The hydraulic passage system has a valve body provided at a side of the hydraulic pump so as to be substantially coaxial with the hydraulic pump. A hydraulic distributor ring is provided so as to be in slidable contact with the valve body.