To provide an air-diffusing pipe for dispersing air supplied from a blower as fine bubbles in water to increase dissolved oxygen, and a method for manufacturing the same, with regard to a device for supplying dissolved oxygen to reaction tanks in facilities for treating sewage and waste water, lakes, ponds, rivers, fish farms, etc. to culture aerobic microorganisms, increase the self-cleaning ability of the water system, and culture fish and shellfish in a high density.

The air-diffusing pipe 1 is formed by strongly and integrally fusion-bonding two or more small bodies 11 and 12 molded of a thermoplastic synthetic resin, which include a plurality of fine air-diffusing ports 21 for generating fine bubbles in water and one or more air supply ports 30 through which air is supplied from a blower, and thus is excellent in the sealability of a bonding portion 14 and can stably maintain an oxygen transfer rate.