of the air moves to the fourth section iv the air bubble generator according to the third embodiment of the present invention varies in distances from the bottom to the lower ends of the compartments for regulation of air flow accordingly as the air in the air bubble generator passes the sections a quantity of air can be regulated since the distribution of air in the air bubble generator is regulated by the compartments a quantity of air bubbles coming out of the plate can be evenly regulated the air bubble generator 400 is constituted with a case 420 a porous member 480 and an air bubble generating plate hereinafter called 34 a plate 34 460 the air bubble generator 400 has space between the case 420 and the plate 460 the porous member 480 is mounted in the space the bottom 440 of the case 420 has an inlet 445 connected with a conduit 80 which is a passageway of compressed air the plate 460 has a plurality of through holes 465 the plate 460 is made with the same process as the first embodiment the porous member 480 has an array of pairs of compartments that is a first pair of compartments 481.