A stirrer comprising: a supporting tube; a hollow housing supported by the supporting tube, the hollow housing including a sucking chamber and a sucking port, wherein the housing is configured to suck a fluid to be processed into the sucking chamber via the sucking port then to introduce it to a stirring chamber via an introducing opening arranged in a comparting wall; a rotating rotor provided with a plurality of blades and accommodated in the stirring chamber; and a screen arranged around the rotor, wherein the screen is tapered towards a central axis of the supporting tube and is arranged around the rotor; wherein the rotor and the screen are provided within the hollow housing, each blade includes an edge portion at an outermost circumferential surface thereof, the screen comprises a plurality of slits in a circumferential direction thereof and a screen member located between the slits that are located in a neighborhood to each other, the edge portion of the blade and the slit have a matching region where they are in the same position and overlapped with each other in a longitudinal direction of the slit, of the rotor and the screen, at least the rotor is rotatable so as to relatively rotate the rotor and the screen thereby ejecting a fluid to be processed in the stirring chamber from inside the screen to outside thereof through the slit as an intermittent jet flow, characterized in that the stirrer is configured to generate a period of static of the fluid to be processed during ejection from the slits and suction from the slits by satisfying following condition 1 and condition 2: Condition 1: in the matching region, a relationship among a width b of the edge portion of the blade in a rotational direction, a widths of the slit in a circumferential direction, and a width t of the screen member in a circumferential direction is shown by b≥2s+t, and Condition 2: in the matching region, a relationship between the width b of the edge portion of the blade in a rotational direction and a maximum inner diameter c of the screen is shown by b≥0.1c. a supporting tube; a hollow housing supported by the supporting tube, the hollow housing including a sucking chamber and a sucking port, wherein the housing is configured to suck a fluid to be processed into the sucking chamber via the sucking port then to introduce it to a stirring chamber via an introducing opening arranged in a comparting wall; a rotating rotor provided with a plurality of blades and accommodated in the stirring chamber; and a screen arranged around the rotor, wherein the screen is tapered towards a central axis of the supporting tube and is arranged around the rotor; wherein the rotor and the screen are provided within the hollow housing, each blade includes an edge portion at an outermost circumferential surface thereof, the screen comprises a plurality of slits in a circumferential direction thereof and a screen member located between the slits that are located in a neighborhood to each other, the edge portion of the blade and the slit have a matching region where they are in the same position and overlapped with each other in a longitudinal direction of the slit, of the rotor and the screen, at least the rotor is rotatable so as to relatively rotate the rotor and the screen thereby ejecting a fluid to be processed in the stirring chamber from inside the screen to outside thereof through the slit as an intermittent jet flow, characterized in that the stirrer is configured to generate a period of static of the fluid to be processed during ejection from the slits and suction from the slits by satisfying following condition 1 and condition 2: Condition 1: in the matching region, a relationship among a width b of the edge portion of the blade in a rotational direction, a widths of the slit in a circumferential direction, and a width t of the screen member in a circumferential direction is shown by b≥2s+t, and Condition 2: in the matching region, a relationship between the width b of the edge portion of the blade in a rotational direction and a maximum inner diameter c of the screen is shown by b≥0.1c. Condition 1: in the matching region, a relationship among a width b of the edge portion of the blade in a rotational direction, a widths of the slit in a circumferential direction, and a width t of the screen member in a circumferential direction is shown by b≥2s+t, and Condition 2: in the matching region, a relationship between the width b of the edge portion of the blade in a rotational direction and a maximum inner diameter c of the screen is shown by b≥0.1c.