To provide an HST capable of increasing the maximum torque while restricting modification to an existing hydraulic system to the minimum scale.

A variable displacement type hydraulic pump P, and two hydraulic motors M1 and M2 actuated by hydraulic oil from that are provided. Hydraulic oil input side ports 25 and 26 of the hydraulic motors M1 and M2 are communicated with and connected to each other, and oil discharge side ports 27 and 28 of them to each other to form a parallel circuit h. The first hydraulic motor M1 is composed in a constant displacement type, and the second hydraulic motor M2 in a variable displacement type. An output combining mechanism A is provided to combine output rotation of the hydraulic motors M1 and M2 to be taken out as combined output rotation. The second hydraulic motor M2 is composed in a two-state changeable type to be capable of forming a first speed state where its swash plate angle is equal to a swash plate angle of the first hydraulic motor M1, and a second speed state where it is 0°.