A device has a plurality of linear sensors which are arranged for at least one
coordinate axis and detect the beam spot. The levels of detected data are measured
by a sensor controller, and the measured levels are compared. Based on the comparison
result, the detection result of one of the plurality of linear sensors is selected.
A coordinate computation unit outputs a coordinate value corresponding to the beam
spot on the basis of the selected detection result. The light-receiving areas of
the linear sensors have an overlapping portion.
