To realize stable starting by suppressing a sudden fluctuation of rotational torque applied to an optical disk during the operation of switching from a constant voltage control to a constant linear speed control.

This spindle motor controller is provided with a torque limitation circuit 109 for inputting a first driving signal d1 (third driving signal d3) as the control signal of a linear speed proportional to the error of the linear speed of a rotation control circuit 103 and suppressing the quantity of its fluctuation during the operation of switching from constant voltage control to constant linear speed control, and a switching signal generation circuit 106 for generating a torque switching signal TW based on the increase/decrease of a difference signal between the third driving signal d3 and a specified value d4. During the operation of switching from the constant voltage control to the constant linear speed control, the fifth driving signal d5 of the torque limitation circuit 109 is selected when the torque switching signal TW is ON 'H', and a spindle motor 112 is driven by the control signal of the linear speed, the fluctuation quantity thereof being suppressed.