In an optical disc, a wobble signal is to be detected by a simple configuration. In the optical disc, the address information, modulated onto a sinusoidal cannier signal by adding even harmonics signals to the sinusoidal carrier signal and by changing the polarity of the harmonics signals, is formed into the wobble signal. In detecting the wobble signal from the optical disc to demodulate the address information, in a method for detecting the wobble signal, an even harmonics signal and data clocks are generated, and the even harmonics signal so generated are multiplied with the reproduced wobble signal. The resulting product signal is integrated every data clock. The sign of the digital information is verified based on the integrated value at an end edge of the data clock.