PURPOSE: To efficiently enable an optical communication between a stationary member and a rotary member at a low cost by providing the rotary member with a means which transmits light beams and the stationary member with a means which reflects the light beams and a receiving means.

CONSTITUTION: The optical data link is equipped with the transmitters 40a-401 which are provided on the rotary member 30 and transmits light beams at a specific angle to the rotary member 30 in a stationary state during the transmission of the light beam and the receiver 50 which is provided on the stationary member 20 and receives the light beam and the reflector 70 which reflects the all light beams to the receiver 50 when the light beams are made incident. The transmitters 40a-401 consist of many laser diodes which are arranged at the periphery of the rotary member 30 and transmit the light beams at the specific angle to the rotary member 30 in the stationary member 30 during the transmission of the light beams, and the reflector consists of a single or double curved-surface mirror which reflects the light beams sent from one or more laser diodes corresponding to the rotational position of the rotary member 30 at the same time.