With an optical head, a stimulating ray beam produced by a stimulating ray source is irradiated onto an image carrier supported on a stage, and light emitted by the image carrier is collected and guided toward a photodetector. At least either one of the optical head and the stage is moved with respect to the other and in two-dimensional directions along a plane parallel with the other. The optical head comprises a concave mirror for reflecting the stimulating ray beam, which travels in parallel with the stage, toward the image carrier, and a lens for converging the stimulating ray beam, which has been reflected from the concave mirror, onto the image carrier. The lens and the concave mirror also guide the light, which is emitted by the image carrier, toward the photodetector.