Wheels of a dump truck are each provided with a travel assembly for transmitting an output of an electric motor to the wheel via a reduction gear unit. The travel assembly is provided with a cooling circuit for cooling lube oil. The cooling circuit has an oil cooler and a recovery oil passage for guiding lube oil from a side of the gear unit to the cooler. The recovery oil passage has an intra-spindle recovery line inserted on a side of an inner periphery of a spindle, a suction pipe extending from the recovery line to a space surrounded by the spindle, the wheel and two spindle-supporting bearings, and communication holes formed in the wheel to communicate the side of the reduction gear unit with the space.