PURPOSE: To provide a driving force transmitting mechanism which transmits the rotational driving force in one direction of a driving source such as a motor by moving a part of a transmission gear train in the axial direction of the gear by manual operation and optionally switching the rotating direction thereof to normal and reverse directions.

CONSTITUTION: This mechanism is provided with an output gear 30 rotated by the motor, an actuating member 60 to which the driving force from the output gear is transmitted through the transmission gear train, and switching means 33, 35 and 36 which switch the rotating direction of the driving force transmitted to the actuating member by moving a part of the transmission gear train along a rotary shaft by the manual operation and increasing or decreasing the odd number of gear train in a driving force transmitting path.