A position-data converter and a motor-drive control device are connected. The position-data converter receives two-phase, sine-wave analog signals da and db from two first magnetic detectors, respectively, and converts these signals da and db to position data. On receiving a positioning instruction, the motor-drive control device calculates the value of current, from the current position signal generated by the position-data converter. The permanent magnets incorporated in a linear motor are used as components of a linear scale, as well.