A disinfection method, a disinfection device, and a disinfecting agent which utilizes light, which can achieve a high disinfection effect within a short time are provided. A disinfecting agent containing catechins is brought into contact with an item to be disinfected, and then the disinfecting agent is irradiated with light. The disinfecting agent preferably comprises an aqueous proanthocyanidin solution produced by polymerizing multiple catechin molecules each having a gallate group. Particularly, the aqueous proanthocyanidin solution preferably has a proanthocyanidin concentration of 0.25 to 4 mg/mL. Light with which the disinfecting agent is irradiated preferably has a wavelength of 350 to 500 nm.
