An agitator includes: an agitation tank that accommodates a fluid to be processed containing particles; a flow blade that agitates the fluid to be processed accommodated in the agitation tank; and a shear blade disposed inside the flow blade at a bottom of the agitation tank to disperse the particles. The shear blade 16 includes a base portion rotating around a predetermined axis and a plurality of blades provided at an edge of the base portion. An angle formed on a downstream side in a rotation direction of the base portion between the blade and a tangent line to an outer periphery of the base portion and each of the blades is 15 degrees or more and 60 degrees or less.