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Minute bubbles have various uses. One of which is water purification. In water purification, additional pumps are necessary to diffuse microbubbles widely throughout the water besides a microbubble generator. Due to this, the consumption of electricity is high. In the previous study, a bladeless mixer was focused on as a new minute bubbles generator for water purification. The bladeless mixer has a very simple shape which is a half-sphere with some holes through it. The mixing is carried out by a jet from each outlet by centrifugal force. Then, as air is sucked from an aeration hole on each a flow channel, small bubbles can be generated. But the distribution and average diameter of the generated bubbles have not been clarified. In the present study, the distribution and average diameter of generated bubbles were investigated. Also, the effect of the shape of an aeration hole and the outlet channel on the diameter of generated bubbles was investigated for fragmentation of generated bubbles. In the experiment, the distribution and average diameter of generated bubbles were measured for 4 aeration types which have different diameter and numbers and for 7 outlet channel types which have step, change of flow path and so on. The conclusions are as follows:(1) The average diameter of bubbles generated by a bladeless mixer is about 140~200 m and the percentage of microbubbles in the water tank is around 40 %. (2) The minute bubbles generated by high shear force on the outlet caused by rotation. (3) The average diameter of bubbles became small using a smaller aeration hole but there is no effect caused by changing number of aeration holes. (4) The shape of the outlet channel influenced the diameter of the generated bubbles. Especially, the average diameter of bubbles decreased about by 10 % with the wall type and edge wall type which have a wall near the outlet causing an impact on the air column.