PURPOSE: To remove current due to counter electromotive force, generated in a spindle motor upon the abnormality of a power source, from the spindle motor by a method wherein a switch means, short-circuit between a coil and an earth, is provided to set the switch means in ON condition when the abnormality of the power source supplied to a motor driving means is detected.

CONSTITUTION: When a power source voltage, supplied to a motor driving circuit 13, is reduced or a power source is intercepted, the operation of the motor driving circuit 13 becomes impossible. In this case, the gate voltage of a FET 15 is biased to Vt. When the FET is put ON, the coil phases 12b, 12c of a spindle motor 11 are short-circuited. The spindle motor 11 is being rotated by an inertia force and current due to counter electromotive force, generated by the rotation, may be consumed at the place of the short-circuit as an energy.