A stable power supply apparatus in accordance with the present invention comprises a secondary battery, a bidirectional chopper circuit and a bidirectional converter, wherein the secondary battery, the chopper circuit and the converter are connected in this order in the direction from the secondary battery side to a system bus line side. Voltage amplifying circuit may include a voltage amplifier and a gain changing unit. A first fold may be disposed upon the first edge and a second fold may be disposed upon the second edge. Syndrome generation is then performed for each column, with the partial syndromes for each column stored in a memory. The delivery phase occurs at a lower pressure than the maximum pressure of the main peak pressure.