In an apparatus for optically reading out through an imaging optics a first image of information by a photodetector. The information is attached to a target. In the apparatus, a marker beam irradiating unit irradiates on a target a marker beam for indicating a field of view of the photodetector on the target. A first pickup unit causes the photodetector to pick up through the imaging optics a second image of the target based on the field of view while the marker beam is being irradiated on the target by the marker beam irradiating device. A position detecting unit detects a position of the marker beam being irradiated on the target with respect to the field of view based on the picked-up second image. A distance determining unit determines a distance between the apparatus and the target based on the detected position of the marker beam.