There is disclosed a liquid ink including a photo acid generating agent that generates an acid upon irradiation with light, a coloring component, and at least one kind of a solvent that is polymerized in the presence of an acid. It is preferable that the amount of the photo acid generating agent contained in the liquid ink falls within a range of between 1 part by weight and 10 parts by weight relative to 100 parts by weight of the solvent, the coloring component consists of a pigment, and the solvent contains at least 50 parts by weight of an acid polymerizable compound, the acid polymerizing compound polymerizing in the presence of the acid, having an alicyclic skeleton and/or an aliphatic skeleton having a viscosity of 50 mPas or less and a boiling point of 150.degree. C. or more under room temperature and atmospheric pressure.