PURPOSE: To deal with the speedup of the revolving speed of a CD driving device by the central processing unit of the same throughput in the data processing circuit of CD-ROM by detecting the completion of the transfer of one sector by the number of transferred data by using a counter, and detecting a synchronizing pattern at a forefront of the next sector.

CONSTITUTION: Every time the data of one byte is outputted from the CD driving device 6 to a buffer memory 2, an address generator 4 increases an address of outputs by '1', and the counter 8 counts the number of the transferred bytes. When the counter 8 detects the number of the bytes of one sector, it stops output to the buffer memory 2, and simultaneously, it informs the central processing unit of this. While the central processing unit 3 executes processing to set the address for outputting the next sector to the buffer memory 2, the synchronizing pattern is sent from the CD driving device 6. When a synchronism detection circuit 1 detects this synchronizing pattern, the output of the data of the next sector to the buffer memory 2 is started.