Two or more solutions comprising an organic pigment solution in which an
organic pigment is dissolved in a good solvent, and a poor solvent
compatible with the good solvent, or a solution of the poor solvent are
allowed to flow through a microchannel in a non-laminar state; and
organic pigment fine particles are deposited from the organic pigment
solution in a course of flowing through the microchannel by changing the
solubility of the organic pigment solution with the poor solvent or the
solution of the poor solvent. As a result, nanometer-scale monodisperse
organic pigment fine particles can be produced in a stable manner.