To maintain motion after launching on the water by launching on the sea-surface with keeping an original position thereof, and to obtain safety at emergency evacuation by making the lifeboat run due to only falling energy, and apart from a mother ship as far as possible due to only inertia.

Considering the total centroid position of a lifeboat 1, when the centroid 11 of the lifeboat 1 passes by a lower end of a sliding way 2, the lifeboat 1 changes from restraint falling to free falling. A guide rail 7 is provided from the bow of the lifeboat 1 to a generally centroid position, at most a 60% length of the lifeboat 1, so as to keep an original position of the lifeboat 1. A hard resin pad is laid on the sliding way 2, and the guide rail 7 is slid. The distance of sliding is made to be small as far as possible, and a friction area is made to be small, so that a specified acceleration can be obtained by the inclination of the sliding way 2.