To easily carry a floating building birth to a mooring place, to easily install the floating building birth at the place, and to easily perform floating and sinking operations.

In this floating building birth 1, a floating body 8 for a front frame is laid and mounted close to front parts of a pair of floating bodies 2 and 3 for floating arranged in parallel at an interval in the longitudinal direction of a hull 21, and a floating body 9 for a rear frame is laid and mounted close to rear parts of the floating bodies 2 and 3. Each of the floating bodies 2 and 3 and the floating bodies 8 and 9 is made of a bar-shaped float formed by a waterproof flexible sheet material to be expanded into a bar-shape by air feeding and to be shrunken into a flat shape by exhaust. At the time of the mooring, a rope 13 for tight biding is connected and fixed to the hull 21, each of the floating bodies 8 and 9 is simultaneously expanded to be pressed on the bottom of a vessel, and each of the floating bodies 2 and 3 is simultaneously expanded and floated so that an upper surface of each of the floating bodies 8 and 9 may be an upper side of a water surface W and horizontally floats and supports the hull 21 to be prevented from being soaked. Each of the floating bodies 8 and 9 mounts and supports the hull 21 and floats and supports the hull 21.