PURPOSE: To absorb displacement due to the lateral motion of a vehicle, and thereby prevent respective sections from being subjected to unresonable force as well as to improve running performance by constituting mounting one end of a main electric motor onto a suspension tube to be capable of absorbing the lateral motion of the vehicle.

CONSTITUTION: A main electric motor is mounted onto a suspension tube 5 integrally formed with the bearing section of an axle 2 at one end, and is also mounted onto a truck frame via vibration-proof rubber 13 at the other end. In this case, mounting one end of the main electric motor 8 onto a suspension tube 5 is constituted to be capable of absorbing the lateral motion of a vehicle. Namely, mounting pieces 15 are arranged on the upper and lower sections of the suspension tube 5, furthermore, two mounting arms 18 are disposed onto the main electric motor 8, and respective friction plates 17 and 19 are concurrently brought in contact with each other. By this constitution, when wheels are laterally displaced, the movements of the suspension tube 5 and the main electric motor 8 are separated with the respective friction plates 17 and 19 slipped at a point where friction force exceeds a specified value.