A bubbly fluid producing method configured to produce a bubbly fluid containing a bubble with a desired bubble diameter, includes applying a shear to a bubbly fluid containing a bubble with a bubble diameter larger than a desired bubble diameter so as to produce a bubbly fluid containing a bubble with a desired bubble diameter. A bubbly fluid producing device configured to produce a bubbly fluid containing a bubble with a desired bubble diameter, includes a first member configured to apply a shear to a bubbly fluid containing a bubble with a bubble diameter larger than a desired bubble diameter so as to produce a bubbly fluid containing a bubble with a desired bubble diameter.