A dump truck provided with a vehicle drive unit comprising: a cylindrical spindle an axial one side of which is attached to a vehicle body and on an inner peripheral surface at an axial other side of which a female spline portion is formed; a wheel that is positioned in the axial other side of the spindle to be disposed on an outer peripheral side of the spindle and on which a tire is attached; wheel bearings (17, 18) that are arranged between the spindle and the wheel to rotatably support the wheel in relation to the spindle; a rotation source located on the axial one side of the spindle; a shaft that is connected to an output shaft of the rotation source, is inserted axially in an inner peripheral surface side of the spindle and projects from the other end side of the spindle; a planetary gear reduction device that is positioned in the axial other side of the spindle to be disposed between the shaft and the wheel and is provided with a plurality of planetary gears rotatably supported by a carrier spline-coupled to the female spline portion of the spindle; and a shaft bearing that is positioned closer to the axial one side than the carrier in the planetary gear reduction device to be disposed on the inner peripheral surface side of the spindle and rotatably supports the shaft in relation to the spindle, on the inner peripheral surface side of the spindle, a retainer is disposed to be positioned, the retainer being formed of a material different from the spindle and retaining the shaft bearing; characterized in that the retainer is provided thereon with a male spline portion spline-coupled to the female spline portion of the spindle; and a radial gap formed between the female spline portion of the spindle and the male spline portion of the retainer is set to be smaller than a radial gap formed between the female spline portion of the spindle and another male spline portion formed in the carrier. a cylindrical spindle an axial one side of which is attached to a vehicle body and on an inner peripheral surface at an axial other side of which a female spline portion is formed; a wheel that is positioned in the axial other side of the spindle to be disposed on an outer peripheral side of the spindle and on which a tire is attached; wheel bearings (17, 18) that are arranged between the spindle and the wheel to rotatably support the wheel in relation to the spindle; a rotation source located on the axial one side of the spindle; a shaft that is connected to an output shaft of the rotation source, is inserted axially in an inner peripheral surface side of the spindle and projects from the other end side of the spindle; a planetary gear reduction device that is positioned in the axial other side of the spindle to be disposed between the shaft and the wheel and is provided with a plurality of planetary gears rotatably supported by a carrier spline-coupled to the female spline portion of the spindle; and a shaft bearing that is positioned closer to the axial one side than the carrier in the planetary gear reduction device to be disposed on the inner peripheral surface side of the spindle and rotatably supports the shaft in relation to the spindle, on the inner peripheral surface side of the spindle, a retainer is disposed to be positioned, the retainer being formed of a material different from the spindle and retaining the shaft bearing; characterized in that the retainer is provided thereon with a male spline portion spline-coupled to the female spline portion of the spindle; and a radial gap formed between the female spline portion of the spindle and the male spline portion of the retainer is set to be smaller than a radial gap formed between the female spline portion of the spindle and another male spline portion formed in the carrier.