Front wheels (3) are attached to transmission devices (30) which are mounted to the vehicle body (2) to be rotatable around vertical axes (27), and rotating means (55) are provided between the side of the vehicle body (2) and the transmission devices (30), whereby the front wheels are steered to turn laterally at substantially right angles. An electric motor (40) is attached to the transmission device (30) to be located under the vertical axis (27). A case body (41) of the electric motor (40) is constructed by an outer case part (41A) and a non-loaded side bracket (41B), and a loaded side end portion of the outer case-part (41A) is connected to the transmission device case body (31). The drive shaft (44) is rotatably supported by the non-loaded side bracket (41B) at one end and by the transmission device case body (31) at the other end. A driving portion (34) provided at the other end side of the drive shaft (44) is operatively connected to an axle (28). As a result, a traveling drive device section can be constructed to be compact with assembling easiness.