In a storage device, before activating a spindle motor (SPM) or continuously from activation until the SPM is stabilized at a target number of rotations, a voltage and temperature monitoring unit monitors the temperature in a disk enclosure unit and the voltage to be applied to an SPM driver. A current limit value calculating unit calculates an optimum current limit value not exceeding a rated current of the SPM driver, and a motor controlling unit controls the SPM driver and changes the current to be applied to the SPM so that the current does not exceed this optimum current limit value.