PURPOSE: To allow highly accurate control of a miniature spindle motor having low inertia whose magnetization error is not negligible.

CONSTITUTION: The spindle motor controller for controlling the rotational speed of the rotor of a spindle motor 3 having the rotor 1 and a stator 2 based on an index signal detected through a detecting element 4 mounted on the stator 2 in order to detect magnetic field of the rotor 1 and output the index signal comprises a memory 5 for storing a plurality of index signals during one revolution of the rotor 1 as reference index signals when the rotor 1 is rotating at a constant speed, and a control section 6 for matching the phase of index signal produced through rotation of the rotor 1 with that of the reference index signal.