A movement detector device consumes less power and provides a high detection reliability. The teeth on a rotating gear are magnetically detected. There are a number of interconnected magneto-resistors MR1 through MRi connected in series, with the series circuit connected between a power supply line and a ground line. There are output signal pickup points P1 through P7 at the connections between the adjacent magneto-resistors. Signals outputted from these signal pickup points P1 through P7 are shifted in their phases by 1/2period with respect to each other. These signals are paired, and each of the paired signals is fed to a differential amplifier circuit to provide signals E1 through E4 as detection signals. In another embodiments, a linear member has a number of magnetic spots which may be detected in the same manner that the gear teeth are detected.