System and method for disk recording

1. Field of the Invention When data recorded on a disk is traced in a reproduction mode, a selection circuit () is switched so as to select data read by said selection circuit (). When a recording decision means () decides start of data recording, said selection circuit () is switched so as to select a reference clock. In this manner, a system clock generated from a system clock generation circuit () is gradually switched from a state which is synchronized with a bit clock to a state which is synchronized with a reference clock. According to the output system clock, recording data written on the disk is synchronized with the recorded data from a position continuous to the recorded data.