PURPOSE: To simplify a structure and reduce a size of a stepless transmission device such as a small-sized power mower by arranging hydraulic pump cylinders perpendicularly to hydraulic motor cylinders, parallelly arranging in respective cases, covering them with respective hydraulic distribution bases, and arranging a hydraulic pump input shaft perpendicularly to a hydraulic motor output shaft.

CONSTITUTION: A left half portion of a device case serves as a pump chamber 4, while a right half portion serves as a hydraulic motor M. The hydraulic pump chamber 6 is partitioned by a cover 6 which composes a hydraulic distribution base, while the hydraulic motor M is partitioned by a similar cover 11. Cylinders 19 are arranged circumferencially in the hydraulic pump chamber 4, and housed in a case for forming a pump P, while an input shaft 8 is arranged on a center portion. In respect to the hydraulic motor M, cylinders 29 are arranged circumferencially in one case so as to form right angles with the hydraulic pump cylinders 19. An output shaft 27 is arranged in the center portion, perpendicularly to the input shaft 8.