An agent for treating various kinds of diseases which contains at least one selected from the group consisting of sexual steroid hormone such as estrogen or its metabolites, its derivative, structural analogues thereof, estrogen acting substance or SERM non-feminizing estrogen (non-hormonal estrogen), and an activator of sirtuin and has a form of eye drops or eye washes, oral preparation, etc. An agent for treating eye diseases which has excellent treatment effects, reduced in side action can be provided.