PURPOSE: To inject air from the entire surface of a blade by boring an air injection hole in the side face of a rotating shaft at its root provided with the blade, furnishing a screen to the blade close to the injection hole in the water flow direction and extending the screen in the width direction of the blade.

CONSTITUTION: A blade 1 is protruded from the rotating shaft 2 connected directly to a power in this spiral or screw aerator. Air is supplied from an air passage by the negative pressure generated in the liq., and the liq. is agitated and aerated. In this case, the shaft 2 is hollowed and utilized as the air passage. A blade 1 is arranged close to the end of the shaft 2, and an air injection hole 5 is bored in the side face of the shaft 2 at its root furnished with the blade 1. A screen is attached to the blade 1 close to the hole 5 in the water flow direction and extended in the width direction of the blade. Consequently, a suction force, etc., due to surface stripping are utilized to inject air from the entire surface without hollowing the blade 1.