Provided is a highly reliable disk array device. Specifically, this disk array device has a number of hard disk drives for respectively storing data, and which converts a first direct voltage supplied to each of the hard disk drives via a common power supply bus into a second direct voltage required by the hard disk drives at each of the hard disk drives, wherein each of the hard disk drives includes a voltage converter for converting the first direct voltage into the second direct voltage; a control unit for controlling the voltage converter so as to suppress the fluctuation of the second direct voltage based on the second direct voltage output from the voltage converter; and a response characteristics switching unit for switching the response characteristics of the control unit against the fluctuation of the second direct voltage so as to improve the response characteristics of the control unit against the fluctuation of the second direct voltage when a transitional voltage fluctuation of the second direct voltage occurs.