An optical recording/reproducing apparatus capable of backing up recorded information in case of an electrical power failure and a recorded information backup method thereof. Management information on recorded data is stored in a local memory such as a static random access memory (SRAM), when data is recorded into an optical storage medium. The management information is updated every predetermined period, and, if data for a corresponding title is completely recorded, the management information stored in the SRAM is recorded onto a certain area of the optical storage medium. If a power failure occurs during the recording of the data, a built-in battery operates and applies a predetermined voltage to the SRAM, so that the management information stored in the SRAM is maintained during the power failure. If the power is re-applied, it is determined whether a recording flag is set in the SRAM, and, if the recording flag has been set, the management information stored in the SRAM is recorded onto the optical storage medium.