A stirrer is provided that can more efficiently achieve shearing applied, by an action of an intermittent jet flow, to a fluid to be processed. The stirrer concentrically includes a rotor including a blade, a partition wall, and a screen, wherein: the screen includes a plurality of slits in a circumferential direction thereof and screen members located between the adjacent slit; by rotating at least the rotor of the two components, the fluid to be processed is discharged from the inside to the outside of the screen as the intermittent jet flow through the slit of the screen; the screen has a cylindrical shape having a circular cross section; an opening of the slit provided on the inner wall surface of the screen is used as an inflow opening; openings of the plurality of slits provided on the outer wall surface of the screen are used as outflow openings; and the width of the outflow openings in the circumferential direction is set to be smaller than the width of the inflow opening in the circumferential direction.