A radiation-curable ink composition contains (A) aminoacrylate at 1 mass % to 10 mass %, inclusive, (B) phenoxyethyl acrylate at 20 mass % to 50 mass %, inclusive, and (C) tetraethylene glycol diacrylate at 1 mass % to 20 mass %, inclusive, in its reaction component, as well as (E) bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide at 3 parts by mass to 8 parts by mass, inclusive, (F) 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide at 3 parts by mass to 5 parts by mass, inclusive, in 100 parts by mass of the reaction component, and (G) diethylthioxanthone at 1 part by mass to 3 parts by mass, inclusive, in 100 parts by mass of the reaction component.