A power supply device comprising: a fuel-cell power device configured to supply a direct current power to one or more load devices using fuel cells as an input source; a control unit configured to control an output from the fuel-cell power device; a load current detection unit configured to detect a current value of a load current supplied to the load devices; and an adjustment unit for shifting an output characteristic representing a relation between an output current and an output voltage of the fuel-cell power device when a power is supplied to the load devices, the output characteristic being a characteristic in which the output voltage monotonically decreases as the output current increases, the power supply device being characterized in that the power supply device further comprises a rate-of-change determination unit configured to determine whether or not a rate of change in the load current is equal to or higher than a threshold value, the rate of change in the load current referring to an amount of change per unit time in the load current detected by the load current detection unit, wherein, the control unit is adapted to, if the rate-of-change determination unit determines that the rate of change in the load currentis lower than the threshold value, shift the output characteristic of the fuel-cell powerdevice by controlling the adjustment unit and control the output current of the fue-cell power device to follow up the load current during a follow-up period immediately after the load current is changed so that the rate of change in the output current of the fuel-cell power device becomes lower than a preset value, and if the rate-of-change determination unit determines that the rate of change in the load current is equal to or higher than the threshold value, keep the output current of the fuel-cell power device constant during a holding period immediately after the load current is changed and, after the holding period has passed, shift the output characteristic of the fuel-cell power device by controlling the adjustment unit and control the output current of the fuel-cell power device to follow up the load current during a follow-up period so that a rate of change in the output current of the fuel-cell power device becomes lower than the preset value. a fuel-cell power device configured to supply a direct current power to one or more load devices using fuel cells as an input source; a control unit configured to control an output from the fuel-cell power device; a load current detection unit configured to detect a current value of a load current supplied to the load devices; and an adjustment unit for shifting an output characteristic representing a relation between an output current and an output voltage of the fuel-cell power device when a power is supplied to the load devices, the output characteristic being a characteristic in which the output voltage monotonically decreases as the output current increases, the power supply device being characterized in that the power supply device further comprises a rate-of-change determination unit configured to determine whether or not a rate of change in the load current is equal to or higher than a threshold value, the rate of change in the load current referring to an amount of change per unit time in the load current detected by the load current detection unit, wherein, the control unit is adapted to, if the rate-of-change determination unit determines that the rate of change in the load currentis lower than the threshold value, shift the output characteristic of the fuel-cell powerdevice by controlling the adjustment unit and control the output current of the fue-cell power device to follow up the load current during a follow-up period immediately after the load current is changed so that the rate of change in the output current of the fuel-cell power device becomes lower than a preset value, and if the rate-of-change determination unit determines that the rate of change in the load current is equal to or higher than the threshold value, keep the output current of the fuel-cell power device constant during a holding period immediately after the load current is changed and, after the holding period has passed, shift the output characteristic of the fuel-cell power device by controlling the adjustment unit and control the output current of the fuel-cell power device to follow up the load current during a follow-up period so that a rate of change in the output current of the fuel-cell power device becomes lower than the preset value.