Patent ID: 7791995

Claim:
An image information detecting apparatus comprising: a semiconductor laser that emits a laser light beam; a light receiving unit that receives a reflected light beam of the laser light beam applied to a color changing layer of an optical disc, the color changing layer being formed from a photo-sensitive material or a heat-sensitive material, and that outputs an electric signal corresponding to the level of the reflected light beam; and a detecting unit that detects image information based on the electric signal, wherein the detecting unit comprises: a holding unit that holds at least one level of a peak level and a bottom level of the electric signal that varies depending on the level of the reflected light beam; and a determining unit that determines whether presence or absence of the image information, or determines a contrast of the image information, depending on the result of comparison of the level held by the holding unit with a reference level, wherein the image information detecting apparatus detects the image information indicating an image from the color changing layer after the image has been formed therein.