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 NH 4 + ; the salt is constituted by combining at least one cation of K + and NH 4 + + with at least one anion selected from the group consisting of Cl - , Br - , I - , ClO - , ClO 2 - , ClO 3 - , ClO 4 - , NO 2 - , NO 3 - , SO 4 2- , CO 3 2- , HCO 3 - , HCOO - , (COO - ) 2 , COOH(COO - ), CH 3 COO - , C 2 H 4 (COO - ) 2 , C 6 H 5 COO - , C 6 H 4 (COO - ) 2 , PO 4 3- , HPO 4 2- and H 2 PO 4 - ; 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.