To provide an optical device capable of suitably managing an adhesion state of an organic substance to an optical member by a photographer.

An optical device includes: an optical member; a photocatalyst layer formed on a light incidence surface of the optical member; foreign matter determination means that determines whether or not a foreign matter is adhered to the photocatalyst layer; light energy measuring means that measures an amount of light energy incident to the photocatalyst layer; light accumulation time measuring means that measures accumulation time of light incident to the photocatalyst layer; storage means that stores the amount of light energy measured by the light energy measuring means and the light accumulation time measured by the light accumulation time measuring means; photocatalyst reaction amount calculation means that calculates photocatalyst reaction amount on the photocatalyst layer after the foreign matter is adhered to the photocatalyst layer; notification means capable of notifying information on the photocatalyst reaction amount; and control means to allow the notification means to notify the information on the photocatalyst reaction amount calculated by the photocatalyst reaction amount calculation means.