To provide a spindle motor control device having no use for a rotational position sensor disposed at a permanent magnet motor and capable of applying a sine wave current to a winding of the motor for energization by a 3-phase PWM signal.

A d-axis current and a q-axis current are computed from current flowing through 3-phase windings Lu, Lv, Lw of the permanent magnet motor, a d-axis current command Idr is computed, based on an electric power Wm of the permanent magnet motor, and a q-axis current command Iqr is computed, based on a current command SI provided from the outside. Besides, when a d-axis voltage Vd and q-axis voltage Vq are computed, based on the d-axis current command Idr, the q-axis current command Iqr, a d-axis current Id and a q-axis current Iq, and when a d-axis induction voltage Ed is computed, based on the d-axis current Id, the q-axis current Iq, and the d-axis voltage Vd, an angular speed ω of a rotor is determined based on the d-axis induction voltage Ed to estimate a rotational position θ of the rotor, based on the angular speed. Moreover, a PWM signal forming device 21 forms the d-axis voltage Vd, the q-axis voltage Vq, and the 3-phase PWM signals Vu, Vv, Vw from the rotational position θ to perform excitation for the windings Lu, Lv, Lw.