The present invention provides a disinfectant that contains olanexidine in a concentration sufficient to exhibit an effective bactericidal effect, and that has hardly any side effects such as skin irritation. Specifically, the present invention provides a disinfectant containing an aqueous solution that contains olanexidine and at least an equimolar amount of gluconic acid, and substantially contains neither an acid other than gluconic acid nor a salt of the acid other than gluconic acid.