[Problem] To enable an increase of fine bubbles in medium liquid.
[Solution] A suction device of the present invention includes a cylindrical portion that is formed of a cylinder with two base surfaces, first surface and second surface, and that flows medium liquid supplied from a plurality of paths, from the first surface toward the second surface, a plurality of introducing portions that introduce the medium liquid from the first surface or from the vicinity of the first surface into the cylindrical portion such that the medium liquid swirls inside the cylindrical portion, and an outlet port provided at or in the vicinity of the center of the second surface.