A running power transmission mechanism for a vehicle for transmitting drive power from a driving source to a pair of steering wheels and a pair of non-steering wheels. A main-HST outputs synchronized drive power to the steering and non-steering wheels. The non-steering wheels are driven differentially by the main-HST through a gear mechanism. A sub-HST changes the speed of the drive power inputted via a steering-wheel drive output shaft and outputs the drive power to the steering wheels. The steering wheels are driven differentially by the sub-HST through a gear mechanism.