PURPOSE: To select advance and retreat with a simple structure which does not require a high-class transmission.

CONSTITUTION: A synchromesh 44 is installed between the advance/retreat gears 37 and 38 and a propulsion shaft 12. When a lever is selected to an advance position by suspending the revolution of the output shaft 11 of a torque converter 10 by a selecting brake 75, the synchromesh 44 is shifted on the propulsion shaft 12 toward the advance gear 37, by a shift fork 45. The connection between the advance gear 37 and the propulsion shaft 12 is completed through the meshing between the advance gear 37 and the synchromesh 44. Then, the selecting brake 75 is released, and the number of revolution of an engine 7 is increased, and then the vehicle advances.