A meandering groove is formed in a digital disk (10) by wobble signals wobbled to reproduce clock signals. An optical head (26) reads the wobbling signals and an address detecting circuit (4) detects an address signal multiplexed with the wobbling signals. A PLL oscillation circuit (24) outputs a clock signal synchronized with the wobbling signals, the data are modulated by means of a modulation circuit (16) based on the clock signal and a timing signal which is generated on the basis of the address signal, and the modulated data are recorded on the disk (10). To reproduce data, an A/D converter (42) converts an RF signal contained in the wobble signals into a digital signal and a demodulation circuit (44) demodulates the data and outputs the demodulated data.