The sealing performance of a stirring device and the abrasion resistance of a seal are improved. A stirring device includes a stirring tank that defines a stirring chamber; a plurality of stirring blades that are disposed in the stirring chamber; a shear blade drive shaft that extends from a lower side of the stirring tank to the stirring chamber and rotationally drives at least one shear blade among the plurality of stirring blades; and a fixed ring and a rotating ring that is disposed radially outside the shear blade drive shaft and seals between the stirring tank and the shear blade drive shaft. A sealing surface of the mechanical seal structure is formed at the same height as or above a lowermost portion of the stirring chamber.