A photo-curing ink composition comprises a photocation-polymerizable substance, a photocation polymerization initiator, and a surfactant having a functional group. The surfactant is selected and the amount thereof is adjusted so that the acid value per 100 g of the ink composition is not more than 150 mg KOH. The surfactant is selected and the amount thereof is adjusted so that the amine value per 100 g of the ink composition is not more than 23 mg KOH. The ink composition is excellent in dispersion performance, storage stability, and curing performance.