An apparatus for detecting the position of an object. The apparatus has an optical device for magnifying or enlarging a plurality of portions on the object, a photoelectric converter adapted for converting the enlarged portion image into electric signals, a plurality of thresholding circuits adapted for changing analogue signals from the respective photoelectric converter into binary signals with a threshold value determined by a signal level given by a first signal holding circuit, a circuit for calculating the threshold value from the analogue signals, a circuit for detecting the approximate position of a specific pattern in the enlarged portion images through a coarse sampling of the binary signals. A circuit for detecting the exact position of the specific pattern through measuring the area of a specific brightness in a plurality of regions in the enlarged portion images, by a fine sampling of the binary signals, and a controller for controlling the operations of respective circuits.