To using resin for a pressure air blowing portion to manufacture a pressure air blower at a low cost.

A series of openings 5 are provided in a hull outside plank 3 at a stem 2 to be extended toward a stern. A sea-chest 8 is mounted inside to encircle the openings 5. In the sea-chest 8, a plural of small air blow boxes 18 made of resin and arranged in lines are fitted. Each air blow box 18 has the rear face open, the front face 18a provided with a number of air blow ports 6 and the side face 18b provided with an air passage 21.