an optical reproducing method for an optical medium including a disk - like substrate , a spiral or concentric - shaped groove structure along a track formed on the disk - like substrate , the groove structure being wobbled in a radial direction of the optical medium , the track being divided into a plurality of units in the track direction by at least one radial boundary line , at least two adjacent units in the radial direction of the optical medium comprise one zone , and the groove structure included in the respective units within one zone having substantially a same number of wobbling . the method includes irradiating an optical spot on the optical medium , detecting a reflected beam from the optical medium , and reproducing information on the optical medium by sing a signal obtained by the reflected beam .