To provide a boat suspension device equipped with a mounting/ removing device having good workability, which can serve for hanging even a boat having a relatively large weight and is composed of component parts having a relatively small weight.

A wire rope 5 paid off from a winch installed on a trolley dispatched from a mother ship and a submarine boat are coupled together by introducing a locking part 27 provided on the wire rope to a hollow 31 from an opening 32 in the fit part 23 provided on the boat and giving a tension to the wire rope 5 by the winch in the condition that the locking part 27 is fitted in the fit surface 35 on the inside of the hollow 31.