PURPOSE: To lay a jib on a deck, to shift a floating crane and to tow it at the time when a marine meteorological condition prosecutes a rough sea by moving the base part of the jig from a bow part to a stern part by sequentially repeating lock release and lock actuation of the pin lock mechanism of a connecting carriage.

CONSTITUTION: It is devised to stabilize a hull 1 and to prevent application of a more than allowable load on a base part 18 of a jig 2 by shifting, towing a floating crane at the time of a rough sea and laying the base part 18 of the jig 2 on a deck 17 of the hull 1 by way of moving the base part 18 of the jig 2 from a bow part to a stern part at the time when the sea is rough and the wind is strong. At this time, only a first carriage 25 is fixed on a rail 23, a hydraulic cylinder 27 is extended to the side of the stern part by a specified stroke, and a second carriage 26 is moved to the side of the stern part by a hole pitch P of the rail 23 with the first carriage 25 as a fixed system. Thereafter, the second carriage 26 is fixed on the rail 23, and the first carriage 25 is moved to the side of the stern part by the hole pitch P of the rail 23 with the second carriage 26 as a fixed system.