To provide an optical disk and an optical disk reproducing device capable of preventing sub information from being illegally copied and altered. An optical disk includes an optical disk substrate preliminarily provided with concave/convex recording marks in order to record the main information; and a reflection film which covers the optical disk substrate and of which the reflection coefficient is changed by irradiating laser light at or above a certain intensity. The reflection film is preliminarily provided with additional marks for recording the sub information by changing the reflection coefficient of the reflection film on a region where the concave/convex recording marks are formed and the sub information is recorded for every predetermined recording unit for recording the main information. The laser light at or above the certain intensity is irradiated onto the region where the sub information is recorded to reproduce the main information and delete the sub information.