A power source apparatus comprising: a direct current power source to output a first voltage; a load driven with a second voltage higher than the first voltage; a booster converter to boost an output from the direct current power source to the second voltage; and a control circuit, arranged to operate at a voltage higher than the first voltage, to control the booster converter. A power storage unit for storing an output from the booster converter is provided, and a reverse current blocking unit is provided between the power storage unit and the load, for preventing supply of electric power stored in the power storage unit to the load. When the booster converter is started, the electric power is supplied from the power storage unit to the control circuit, and when the booster converter has started, the electric power is supplied from the booster converter to the control circuit.