To provide a mooring buoy system capable of obtaining the tension of a mooring rope with a simple structure, and taking a long maintenance span.

The mooring buoy system includes a mooring buoy 12 afloat on the sea, a monitoring room 32 disposed on the land, and a mooring rope for connecting the mooring buoy 12 and a ship to each other. The mooring buoy 12 includes an inclination angle detection means 18 for detecting its inclination, and a radio communication means 14 for transmitting detected inclination information to the monitoring room 32. The monitoring room 32 includes a radio communication means 34 for receiving the inclination information transmitted from the mooring buoy 12, a calculation means 38 which calculates the tension to be applied to the mooring rope based on the acquired inclination information and a preliminarily calculated information on the buoy to be to be applied to the mooring buoy 12, compares the calculated tension with the predetermined threshold, and determines whether the tension value is larger than the threshold, and an alarm means for issuing an alarm when it is determined that the tension value is larger than the threshold.