In a robot system, a data amount of operation information (log) to be transferred or recorded is reduced, thereby enabling the operation information (log) to be transferred or recorded with a low load. The system has a control unit for controlling the operation of a robot of a robot device and transfers a log regarding the robot operation to a managing terminal. While making the robot operative, the control unit generates log data regarding the robot operation and stores into a short-term storage log recording unit (temporary storage device) (log data generating step). When log transfer timing comes, a part of the log data stored in the recording unit (temporary storage device) is extracted and transferred as a log to a log storage device in accordance with the robot operation (log transferring step).