Oka Binzan was a samurai serving the Hiroshima clan. His real work was not related to the production of paintings; he was mostly involved in promoting the cultural policies of the clan to which he belonged and conveying the wishes of the clan lord to the other officials. This paper clarifies Oka Binzan's official role-one which has not been detailed in any study on the matter to date-and confirms that he accomplished much of his painting in the course of his duties as a public official for the clan and that this was atypical for the samurai during that era.