The requested data is read from a DVD disk by interruption in ST46. Then, the ID information for indicating the leading end of the data, and the result of the identification by use of the EDC for indicating whether or not the data is correct are stored in ST47. When the disk is identified as a DVD-video disk and the flag is set in ST 48, and also when the number of times N of retries is identified as being larger than NR in ST50 and the read data is not identified as control data in ST51, data transmission is performed. When no flag is set, the disk identification is performed based on whether or not the data at a predetermined position on the logical format has predetermined data in ST49. When it is identified that an error has been detected in ST52 and also when the number of times N of retries becomes larger than NS in ST53, the occurrence of an error is announced.