PURPOSE: To compress the air in an air pressure chamber and feed it as the high-pressure air by storing a bag body in an enclosed hollow container to form the air pressure chamber and a water pressure chamber, feeding the air into the air pressure chamber, and applying the water pressure into the water pressure chamber.

CONSTITUTION: When a fan 31 is operated and the air is fed to the air pressure chamber 12 of a compressor main body 1 made of an enclosed hollow container via an intake pipe 3 and an intake valve 32, a bag body 2 is expanded, and a large quantity of air is stored in the air pressure chamber 12. As the volume of the air pressure chamber 12 is increased, the volume in a water pressure chamber 11 is reduced on the contrary. When a drain valve 61 is opened and a feed valve 52 is closed on the other hand, the water in the water pressure chamber 11 is discharged to a storage tank 62. The drain valve 61 and the intake valve 32 are closed, and an air valve 41 and the feed valve 52 are opened on the other hand. The water in the storage tank 62 is sucked with a feed pump 51 and fed to the water pressure chamber 11 via a feed pipe 5. The air in the air pressure chamber 12 is then compressed and fed through an air pipe 4 as the power.