Ink-jet printing with fixing ability, while maintaining printing qualities such as OD and sharpness at high levels, can be achieved by using an ink containing a self-dispersing pigment as a coloring material without using a dispersant and a treating liquid for insolubilizing the coloring material. Benalkonium chloride (G50) having one cationic group in the molecule is used as the insolubilizing agent in the treating liquid. As a result, the cationic group is completely bonded to the anionic group of the pigment particle, thereby producing a cohesive force between pigment particles.