To provide a steering vehicle wheel driving unit having an excellent maintenance property while improving a steering property of a steering wheel, and a four-wheel drive vehicle equipped with it.

This steering vehicle wheel driving unit 15 comprises a housing 28 supporting a single axle 35, a hydraulic motor for driving the axle installed in the housing 28, and front wheels 36, 36 as single steering wheel fixed to ends of the single axle 35. The housing 28 is rotatably mounted to a vehicle frame 2 via a king pin 27, and the hydraulic motor 10 is of a variable displacement type. A movable swash plate 53 of the hydraulic motor 10 is constituted so as to be inclined between the king pin 27, the housing 28 and the vehicle frame 2 by relative rotation in steering.