A hydraulic four-wheel driving apparatus is provided for a vehicle having a pair of left and right unsteerable wheels and a pair of left and right steerable wheels. The hydraulic four-wheel driving apparatus comprises: a transmission casing supporting the unsteerable wheels; a hydraulic pump disposed integrally with the transmission casing, the hydraulic pump being driven by a power source outside the transmission casing; a first hydraulic motor for driving the unsteerable wheels fluidly connected to the hydraulic pump, the first hydraulic motor being disposed integrally with the transmission casing; and a second hydraulic motor for driving the steerable wheels fluidly connected to the hydraulic pump, the second hydraulic motor being disposed integrally with the transmission casing and disposed on one side of the first hydraulic motor toward the steerable wheels.