In order that a hydraulic pump and a hydraulic motor of a hydrostatic transmission hitherto disposed to the exterior are attached to a hydrostatic transmission support member provided in a mission case, a charging pump hitherto attached to the hydraulic pump at the hydrostatic transmission is also attached to the hydrostatic transmission support member, and an oil filter hitherto attached to the outside of mission case is disposed therein, they are interposed between the lower surface of hydrostatic transmission support member and the charging pump. Furthermore, an outward takeout pump also is supported in the mission case.