1. An optical reproducing method for an optical medium including a disk-like substrate, a spiral or concentric-shaped groove structure along tracks formed on the disk-like substrate, each of the tracks being divided into a plurality of units, each of the units including a blank portion of the groove structure along the track in a circumferential direction of the track, the blank portion being a non-groove portion, and the groove structure being wobbled in a fixed cycle in a radial direction, the fixed cycle of the wobble continuing in the circumferential direction along the track, wherein when the wobble is formed on the blank portion in the circumferential direction of the track as the wobble formed on the groove structure and the blank portion is formed so that a phase of the wobble is formed on the groove structure, the blank portion is formed so that a phase of the wobble formed on the blank portion is continued with a phase of the wobble of the groove structure within another unit adjacent to the blank portion, the method comprising the steps of: irradiating an optical spot on the optical medium; detecting a reflected beam from the optical medium; and reproducing information on the optical medium by using a signal obtained by the reflected beam.