Disclosed herein are an ink containing a self-dispersible pigment and a salt, wherein the self-dispersible pigment is a pigment to the surface of a particle of which a functional group containing at least a group having a hydrogen bonding property and two phosphonic acid groups is bonded, counter ions of the two phosphonic acid groups containing one of K+ and NH4+; the salt is constituted by combining at least one cation of K+ and NH4+ with at least one anion selected from the group consisting of Cl−, Br−, I−, ClO−, ClO2−, ClO3−, ClO4−, NO2−, NO3−, SO42−, CO32−, HCO3−, HCOO−, (COO−)2, COOH(COO−), CH3COO−, C2H4 (COO−)2, C6H5COO−, C6H4(COO−)2, PO43−, HPO42− and H2PO4−; a cation concentration in the ink is 0.04 mol/L or more; and the viscosity of a liquid obtained by evaporating 15% by mass of the ink is less than 3.5 mPa·s at 25° C.