PURPOSE: To obtain a small-sized measuring device for extent of shift which works on a single optical mark, by projecting the light to the optical mark through an optical fiber and counting the outputs of a pair of light receiving fibers arrayed in the shifting direction of the optical mark after converting these outputs into pulse signals.

CONSTITUTION: An optical mark 1 containing reflective surfaces 3 and nonreflective surfaces 2 arranged alternately with an equal pitch is irradiated by the light given from a light source 5 via a projecting optical fiber 4c. The light reflected on the surface 3 is detected by light receivers 6a and 6b via light receiving fibers 4a and 4b. With this output of detection, the shifting direction of the mark 1 is detected via a direction detector 8. At the same time, the pulse is produced every time the mark 1 passes through the surface 3. These pulses are counted by an up-down counter 9 and then converted into analog signals through a D/A converter 10 to be used as the recording signals for an oscillogram, etc. In such a way, a small-sized measuring device for extent of shift which works on a single inexpensive optical mark can be obtained.