PURPOSE: To perform the feed of air with a pressure and the feed of air for a long time by means of a device of simple constitution without consuming a resource, such as electricity.

CONSTITUTION: An air chamber 3 surrounded with a float 30 floating on a water surface 90, a flexible air chamber body 31 attached to the float 30, and a cover 32 attached to the body 31 comprises the above devices. The cover 32 is securely held and the air chamber is formed such that an internal volume is fluctuated through vertical movement of the float 30 owing to waves. A feed pipe 4 and an exhaust pipe 5 are connected to the air chamber 3 through a feed valve 41 through which air is allowed to pass only in one-way and an exhaust valve 51.