A curing accelerator can exhibit good curing acceleration performance and is excellent in storage stability, while maintaining sufficient pot life in a curing reaction of radical-polymerizable resins, and a radical-polymerizable resin composition uses the curing accelerator. The curing accelerator for radical-polymerizable resins includes a metal-containing compound (A), a thiol compound (B) and an aprotic solvent (C) having a dielectric constant of 10 or less, wherein the metal-containing compound (A) is one or more compounds selected from a metal soap (A1) and a β-diketone skeleton-having metal complex (A2), the thiol compound (B) is one or more compounds selected from a mono-functional primary thiol compound (B1), a secondary thiol compound (B2) and a tertiary thiol compound (B3), and the content of the aprotic solvent (C) is 10 to 1,000 parts by mass relative to 100 parts by mass of the total of the metal-containing compound (A) and the thiol compound (B).