The present invention provides an optical transmission system that optically transmits an optical signal between a camera adaptor provided to a video camera and a base station provided at a position remote from the video camera. In the optical transmission system, the camera adaptor includes a control signal input unit that receives a control signal including a return signal component, a video selecting unit that outputs, to the exterior, the camera video signal component of the first electric signal of the return video signal component of the second electric signal based on a state of the return signal component, and a control signal separating unit that outputs the control signal other than the return signal component.