A curable composition that can be cured at low temperature in a short time regardless of the type of epoxy compound that is mixed therewith, and has a long pot life; an adhesive comprising said curable composition; a method for producing a fiber-reinforced composite material that uses the curable composition; and a fiber-reinforced composite material containing a matrix comprising the curable composition. A curing agent mixture composition that can be cured at low temperature and in a short time, and provides the curable composition with a long pot life. An epoxy compound (A) and an imidazole compound (B) are blended in with the curable composition. In addition, the imidazole compound (B) and at least one type of crosslinking agent (C) are blended in with the curing agent mixture composition.