PURPOSE: To reduce the hydraulic resistance of a ship upon sailing, by jetting compressed air form the bow section of a ship into the water in the front, in the advancing direction, of the ship to produce air bubbles in the front of the hull of the ship.

CONSTITUTION: Compressed air is fed from the bow of a ship into the water in the front, in the advancing direction, of the ship to produce air bubbles in the front of the hull of the ship. Then, an air layer is formed between the water and the outer shell of the hull, accompanying with the advance of the ship. Thereby, it is possible to aim at reducing the hydraulic resistace of the ship which occurs upon sailing.