Abstract: A semiconductor integrated circuit for signal processing of an optical disk of a write-once type has an EFM demodulating circuit for demodulating an EFM-modulated EFM signal read out of the optical disk; an EFM modulating circuit for EFM-modulating data written to the optical disk; an ATIP demodulating circuit for demodulating an ATIP signal read out of the optical disk; a CLV control circuit for outputting a signal for controlling rotation of the optical disk based on the EFM signal or the ATIP signal; a subcord forming arithmetic circuit for extracting a subcord from the EFM signal and performing a CRC operation of the subcord, the subcord forming arithmetic circuit performing the CRC operation with respect to the data written to the optical disk and forming a subcord; a CIRC modulating/demodulating circuit for detecting and correcting an error in CIRC signal from the EFM-demodulated signal and adding a CIRC error correction code to the data written to the optical disk; an interface circuit for outputting a