A mixer of the rotor-stator type that includes a stator having a plurality of openings and a rotor disposed on the inner side of the stator and spaced by a predetermined gap away from the stator is described, wherein the mixer that is capable of improving the shearing stress applied upon the liquid being processed and provides the higher performance is proposed. The stator includes a plurality of stators each having a different circumferential diameter, and the rotor is disposed on the inner side of the plurality of stators and spaced by the predetermined gap away from the stators so that the stators and the rotor can be brought closer to or farther away from each other in the direction in which the rotary shaft of the rotor extends.