A storage device and its control method are described, according to which a bias voltage to be supplied to a memory cell array is selected from boosted voltages which are increased from an external voltage and non-boosted voltages which are not increased from the external voltage. In the period during which a DC-DC converter section supplies a boosted voltage increased from the external voltage to an internal bias line for supplying a bias voltage to the memory cell array, a non-boosted voltage supply section for supplying a non-boosted voltage equal to or less than the external voltage is in its inactive state. In the period during which the non-boosted voltage supply section supplies a non-boosted voltage to the internal bias line, the DC-DC converter section is in its inactive state. In the period during which a boosted voltage is supplied to the internal bias line, the DC-DC converter section is used for ensuring sufficient power supply ability, and in the period during which the non-boosted voltage is supplied to the internal bias line, the DC-DC converter section can be kept in its inactive state. Thus, the power consumed by the DC-DC converter section can be saved in the period during which the supply of a boosted voltage is unnecessary.