To provide a driving force transmitting mechanism which can be manufactured at a low cost, can be reduced in size and weight, and does not consume much electric power and a card transporting mechanism suitable for card readers by using the transmitting mechanism.

The driving force transmitting mechanism which is constituted to selectively transmit the rotation of a motor 30 to two driving systems 37 and 38 is constituted in such a way that first and second driven-side rotary gears 40 and 41 are provided coaxially with a driving-side rotary gear 39 which is rotated by the motor 30 and planetary gear members 42 which are meshed with the driven-side rotary gears 39 and 41 are attached to the driving-side rotary gear 40. Then a selective locking means 43 which selectively locks one of the driven-side rotary gears 40 and 41 is provided and the driving systems 37 and 38 are connected to the gears 40 and 41 respectively.