The invention is for a mooring device (11) for a flap-gate breakwater (1) having a water blocking door body (2) that pivots about a horizontal axis. The mooring device (11) comprises a mooring hook (15) that controllably engages and disengages a gate mooring member (2b) of the door body (2) during mooring and raising operations. The mooring hook (15) is operated by a control device (21), making it possible to adjust the mooring hook position in a short period of time.