PURPOSE: To obtain a desired spot by light for erasing by using a lightweight object lens by a method wherein the size of the spot is set in such a way that the light for erasing can erase two or more adjacent recording tracks.

CONSTITUTION: As an optical recording medium 1, a recording layer 3 is formed after a glass substrate 2 is coated with a mixture which is composed of a photochromic material, polystyrene and a solvent, and, after that, a reflection layer 4 such as copper is applied and formed by a vacuum deposition method or the like. Light for recording is irradiated through object lenses 9, 10 and records information. Light for erasing is irradiated through an object lens 12 and erases the information. A spot 20 by the light for erasing is scanned by being stretched over at least two or more recording tracks 21 formed by using the light for recording. Thereby, the spot 20 by the light for erasing may be large, and it is possible to easily obtain the spot 20, by the light for erasing, which has a desired size.