To carry out the aeration by setting simply a device on a piping line without using a mechanical equipment for agitation, utilize simultaneously dynamic activities under water generated by agitating and mixing fine air foams under water and carrying out effectively the extrusion of inorganic minerals or the like.

This device is constituted of a main body case 2, an inlet cover case 3, an outlet cover case 4 and piping parts 5, and when water flowing on a pipeline and air introduced from the piping are passed through a mixer 7 provided in the main case 2, air is dispersed finely under water and aeration is carried out. Then fine air foams in the agitated state are permeated into a water quality improving substance 9 and the extrusion of minerals and the like is carried out effectively.