A hydraulic wheel-drive working vehicle according to the present invention makes it possible to change a driving state by a driving-mode switching valve between a right-left differential-lock driving state in which a pair of driving wheels are driven in an independent manner to each other with hydraulic fluid discharged from a hydraulic pump and having respective amounts defined by a flow dividing/combining mechanism and a right-left differential driving state in which the pair of left and right driving wheels are driven in a hydraulically differential manner to each other, and also to supply the hydraulic fluid from the hydraulic pump to the pair of hydraulic motors without being subjected to fluid load of the flow dividing/combining mechanism at the right-left differential driving state, thereby enhancing transmission efficiency at the right-left differential driving state.