Patent ID: 8294890

Claim:
A device for inspecting both sides of surfaces of a magnetic disk to detect defects thereon, comprising: a table unit that is capable of rotating and moving the magnetic disk with the magnetic disk mounted thereon; a front-side defect detecting section that optically detects a scratch and a defect that are present on a front surface of the magnetic disk mounted on the table unit; a back-side defect detecting section that optically detects a scratch and a defect that are present on a back surface of the magnetic disk; a processing section that processes an inspection result obtained by the front-side defect detecting section and an inspection result obtained by the back-side defect detecting section; and an output section that outputs the inspection results processed by the processing section, wherein the back-side defect detecting section includes: a laser light source that emits a laser beam; a light collecting section that collects scattered light by using a Fresnel lens, exclusive of regularly reflected light, the scattered light and the regularly reflected light being included in reflected light from the back surface of the magnetic disk that has been irradiated with the laser beam emitted by the laser light source; a first photoelectric converter that detects the scattered light that has been collected by the light collecting section; and an optical path changing section that reflects the laser beam emitted by the laser light source to change an optical path of the laser beam and thereby to direct the laser beam toward the back surface of the magnetic disk and that reflects the scattered light that has been collected by the Fresnel lens included in the light collecting section to change an optical path of the scattered light and thereby to direct the scattered light toward the first photoelectric converter.