To exercise a fail-safe function by detecting the disconnection of the other phase at the time when stored information on the input phase of each string of pulse signals from a pulse generator continuously becomes the information of the same phase.

A control unit ECU sequentially captures pulse signals Pa and Pb of both phases from a pulser P through the use of the two-phase type pulser P to generate two strings of pulse signals with a phase difference of 90° according to the rotation of a motor M so that the open and closed locations of window glass can be, for example, obtained in trace amounts of the order of a few millimeters. At the time of counting each of the leading edges and trailing edges of the pulse signals Pa and Pb of each phase as a trigger, information on the input phase of the pulse signals is captured in internal memory as sequentially storing and updating it, and the breaking of the string of pulse signals of the other phase is detected at the time when the information stored in the internal memory continuously becomes the information of the same phase.