To reduce a weight of HST by forming a reinforcing rib on an outer face of a case rationally, reducing a wall thickness of the case without reducing the strength thereof, and reducing a weight of a casing which is heavy.

Hole parts 18, 19 for supporting swash plate shaft are formed on respective right and left case horizontal wall faces 11c, 11d which oppose mutually in adjacent to an opening 11f for mounting port block in a baglike HST main body case 11, and a longitudinal rib 22 on an outer face of the main body case 11 over fringe ribs 18a, 19a of them is provided by extending it in the direction in which it crosses a pump rotary shaft core at a position close to the opening 11f for mounting port block. A horizontal rib 23 formed integrally on the outer face of the main body case 11 in the direction along the pump rotary shaft core is connected with a boss part 11g for screwing and fixing port block on the case horizontal wall faces 11c, 11d and is formed in a condition in which it crosses the longitudinal rib 22.