The invention provides ink which is best suited for inkjet printing of a printed substrate. The ink is a photo polymerizing type water-base ink including at least a colorant, a photo polymerization resin, a photo initiator, and a water-base solvent. The photo polymerization resin includes oligomer particles in an emulsion state and monomers which reside in the oligomer particles. The water-base ink contains, with content ratio in terms of the percentage weight, 5% of ethyleneglycol, and between 0.1% to 10% of 2-pyrrolidone and N-acryloyl morpholine combined.