In a hydraulic transmission for driving and steering wheels of a vehicle, which has at least a first pair of laterally disposed wheels, a first hydraulic pump is operatively connected to a driving source with inlet/outlet ports respectively and fluidly connected to a high pressure side and a low pressure side of the parallel fluid passages. A second hydraulic pump is operatively connected to the driving source and having inlet/outlet ports respectively and fluidly connected to high and low pressure sides of the fluid passages between the second pair of hydraulic motors. The first hydraulic pump is of a variable displacement type that varies the amount of hydraulic fluid to be discharged and supplied, based upon the displacement amount of a first output adjustment member, in which the displacement amount is varied by operating the first output adjustment member via a driving-speed operation member. The second hydraulic pump is of a variable displacement type that varies the amount of hydraulic fluid to be discharged and sucked, based upon the displacement amount of a second output adjustment member, in which the displacement amount is varied by operating the second output adjustment member via a steering operation member. Rotational power is input from each of the second pair of hydraulic motors to a corresponding one of the output shafts of the first pair of hydraulic motors by a magnitude corresponding to the operational amount of the steering operation member in a different rotational direction from each other.