A power transmission apparatus and an image forming apparatus are provided. The power transmission apparatus of transmitting driving power to first and second movable members includes a driving unit which receives the driving power from a driving power source, and which rotates in forward and backward directions, a first driven unit which transmits the driving power to the first movable member, an elastic clutch which is provided between the driving unit and the first driven unit to selectively allow the driving power from the driving unit to be conveyed to the first driven unit based on the direction of the driving power, and a second driven unit to convey the driving power to the second movable member regardless of the direction of the driving power so as to allow the second movable member to rotate bi-directionally. The first movable member may be, e.g., a photosensitive body. The second movable member may be, e.g., exit rollers for ejecting processed printing medium out of the image forming apparatus.