which is designated by the device command signal 105 the number of sectors which are not yet processed is compared with a capacity four sectors in the embodiment of the memory circuit 9 when the number of the sectors which are not yet processed is larger than the capacity of the memory circuit 9 four sectors are made to one data processing unit and each data processing unit having four sectors is processed at a time step 411 the data demodulation process and error correction process are performed with respect to each sector of the data processing unit by the microprocessor 4 first data demodulation process with respect to the start sector s 0 of the data processing unit is performed t 1 t 2 second the data demodulation process and data correction process are performed in parallel with respect to successive sectors s 1 s 2 and s 3 and finally the error correction process is applied to the final sector s 3 of the data processing unit step 412 then the data transfer process is successively performed with respect to each sector of the data processing unit by the microprocessor 4 and data reproduction operation with respect to the data processing unit is completed step 413 then the block count which is designated by the device command 105 is compared with the number of sectors which are already processed after completion of the data reproduction operation with respect to entire sectors the command status signal 112 is transmitted from the microprocessor 4 to the host computer 3 on the other hand when the sector which has not yet been operated on by the data reproduction operation remains the flow advances to step 411 and the data reproduction operation is applied to the subsequent data processing unit from a.