To effectively generate fine air bubbles and large air bubbles inside a water tub by simple device constitution and a control means.

An air bubble generator comprises: an air bubble jetting device 13 composed of a microbubble nozzle 14 and a big air bubble nozzle 16 to be arranged in the water tub 2; a pump 1 for sucking, pressurizing and circulating the water 3 of the water tub 2; an air mixing device 7 provided in the intake part 5 of the pump 1; a first flow path 15 provided with an air dissolved water generator 19 for dissolving air in pressurized water 21 mixed with the air discharged from the pump 1, separating and removing undissolved air and generating air dissolved water 24, for supplying the generated air dissolved water 24 to the fine air bubble nozzle 14; and a second flow path 17 for supplying the pressurized water 21 mixed with the air discharged from the pump 1 through a switching valve 28 to the big air bubble nozzle 16.