A motor driver device includes: a detector that detects a polarity inversion timing of a current flowing through a coil of a predetermined phase of a motor; a drive control signal generator that generates a pulse-width-modulated or pulse-density-modulated drive control signal for each phase based on the detection result; and a drive voltage supply that supplies a drive voltage corresponding to the drive control signal to a corresponding coil, wherein the drive control signal generator includes a prediction processor configured to set a detection prediction interval based on two or more previously detected polarity inversion timings, and executes a frequency variable control to set a variable target frequency to be higher in the detection prediction interval than outside the detection prediction interval, the variable target frequency being a frequency of the pulse-width-modulated drive control signal or a reciprocal of a minimum pulse width of the pulse-density-modulated drive control signal.