To provide a racing course constitution system provided with a buoy supporting rope traction mechanism capable of coping with the demand that the tension of a rope for supporting a buoy is required to be kept fixed at all times in order to keep the buoy for constituting the lane of a racing course at the same position at all times regardless of the change of a water level.

A plurality of lane wires 23 to which the appropriate number of branch ropes 30 to which lane buoys 33 are attached are fixed are arranged side by side, lane constitution poles for holding an interval are equipped at both end parts of them in a direction perpendicular to the lane wires 23 and the end parts of the lane wires 23 are fixed to the ground and/or in the water respectively individually or together. Normally, the end part supporting part of the lane wire 23 is made vertically movable corresponding to the change of the water level.