PURPOSE: To prevent a mooring chain from being broken by a method wherein changes in a tension exerted on the chain can be alleviated, when mooring a floating structure.

CONSTITUTION: A pair of mooring dolphins 2 are fixedly placed at the surface of the sea at positions spaced from the floating body 1 by a predetermined distance on both sides of the body 1, while a chain guide 4 is provided at the center of the upper surface of the body 1 and chain stoppers 5 are provided on both sides of the chain guide 4. Both ends of the single mooring chain 6 are fixed to the two dolphins 2 respectively, while passing the middle part of the chain 6 through the guide 4 and the stoppers 5 on the body 1. Accordingly, the changes in the tension exerted on the chain can be alleviated.