An ink is provided which suppresses the influence of the kinds of recording media on the image quality, is excellent in image quality, effectively inhibits the occurrence of bleed upon the formation of color images, is excellent in long-term shelf stability and stably forms high quality images. The ink contains at least one salt selected from the group consisting of (M 1 ) 2 SO 4 , CH 3 COO(M 1 ), Ph-COO(M 1 ), (M 1 )NO 3 , (M 1 )Cl, (M 1 )Br, (M 1 )I, (M 1 ) 2 SO 3 and (M 1 ) 2 CO 3 , wherein M 1 represents an alkali metal, ammonium or organic ammonium, and Ph represents a phenyl group, and a self-dispersing anionic carbon black having a functional-group density of at least 1.8 (µmol/m 2 ) on its surface.