A voltage smoothing circuit for smoothing a voltage outputted from a power supply portion, the voltage smoothing circuit comprising: a first smoothing capacitor (C21a) and a second smoothing capacitor (C22a) that are connected in series to each other and are connectable in parallel to the power supply portion; a first balancing resistor that is connected in parallel to the first smoothing capacitor (C21a); a second conduction regulating portion that is connected on a current path in parallel with the second smoothing capacitor (C22a) and configured to conduct current in one direction on the current path in a case where a voltage equal to or greater than a second predetermined voltage has been applied; a second balancing resistor that is connected on the current path in such a way as to become in parallel with the second smoothing capacitor and in series with the second conduction regulating portion, characterized by a first auxiliary resistor that is connected in parallel to the second conduction regulating portion or a second auxiliary resistor that is connected in parallel to the second conduction regulation portion and the second balancing resistor connected in series to each other, wherein current flows in one direction to the second balancing resistor in a case where a voltage equal to or greater than the second predetermined voltage has been applied to the second conduction regulating portion, wherein the resistance value of at least one of the first balancing resistor and the second balancing resistor is decided in such a way as to satisfy a condition where a first end-to-end voltage representing the end-to-end voltage of the first smoothing capacitor becomes lower than the rated voltage of the first smoothing capacitor and a second end-to-end voltage representing the end-to-end voltage of the second smoothing capacitor becomes lower than the rated voltage of the second smoothing capacitor, the second predetermined voltage is substantially the same as or less than the second end-to-end voltage; the second predetermined voltage is lower than the rated voltage of the second smoothing capacitor (C22a), and the second conduction regulating portion is configured to maintain its inter-terminal voltage at the second predetermined voltage in a case where a voltage equal to or greater than the second predetermined voltage has been applied. a first smoothing capacitor (C21a) and a second smoothing capacitor (C22a) that are connected in series to each other and are connectable in parallel to the power supply portion; a first balancing resistor that is connected in parallel to the first smoothing capacitor (C21a); a second conduction regulating portion that is connected on a current path in parallel with the second smoothing capacitor (C22a) and configured to conduct current in one direction on the current path in a case where a voltage equal to or greater than a second predetermined voltage has been applied; a second balancing resistor that is connected on the current path in such a way as to become in parallel with the second smoothing capacitor and in series with the second conduction regulating portion, characterized by a first auxiliary resistor that is connected in parallel to the second conduction regulating portion or a second auxiliary resistor that is connected in parallel to the second conduction regulation portion and the second balancing resistor connected in series to each other, wherein current flows in one direction to the second balancing resistor in a case where a voltage equal to or greater than the second predetermined voltage has been applied to the second conduction regulating portion, wherein the resistance value of at least one of the first balancing resistor and the second balancing resistor is decided in such a way as to satisfy a condition where a first end-to-end voltage representing the end-to-end voltage of the first smoothing capacitor becomes lower than the rated voltage of the first smoothing capacitor and a second end-to-end voltage representing the end-to-end voltage of the second smoothing capacitor becomes lower than the rated voltage of the second smoothing capacitor, the second predetermined voltage is substantially the same as or less than the second end-to-end voltage; the second predetermined voltage is lower than the rated voltage of the second smoothing capacitor (C22a), and the second conduction regulating portion is configured to maintain its inter-terminal voltage at the second predetermined voltage in a case where a voltage equal to or greater than the second predetermined voltage has been applied.