To solve the problem that a large-sized high pressure pump is required as a conventional air bubble generator in order to finely divide air and hot water though a high pressure jet nozzle to mix them and stable fine air bubbles can not be generated because a shuttle valve is used in an air suction part. SOLUTION: The nozzle of a fine air bubble generator is constituted so that flow channel forming members 32 and 33 and 34 forming a fluid flow channel along with a nozzle casing 30 are provided in the nozzle casing 30 of a nozzle main body 10 and a barrier wall 35 is provided ON the downstream side of the flow channel and the flow channel housing a granular material 36 is formed ON the downstream side of the barrier wall 35. The flow channel formed by the nozzle casing 30 and the flow channel forming members 32 and 33 and 34 has a ring shape and can efficiently stably generate fine air bubbles to provide the air bubble generator using a small-sized pump and having stable capacity and high reliability.
