PURPOSE: To perform an easy and precise position detection by providing first and second marker detectors, a narrow pulse signal generating means, a count signal generating means and an UP/DOWN counter.

CONSTITUTION: In a moving quantity detecting device 10, a DOWN signal is generated by a count signal generating means 5 synchronously with both AS1, AE1 signals generated by a narrow pulse signal generating means 3 when a switching command signal is in low state, and decrement of the DOWN signal is performed by an UP/DOWN counter 7. When the switching command signal is in high state, an UP signal is generated by the generating means 5 synchronously with both the AS1, AE1 signals generated by the generating means 3, and increment of the UP signal is performed by the UP/DOWN counter 7. Therefore, the detecting device 10 counts both the AS1, AE1 signals generated every unit moving quantity of a moving body to make the position detecting resolution of the moving body more precise while it has a simple structure, and detects the precise position of the moving body.