Switching power supply

A switching power supply comprising:

• rectifying means for rectifying an AC power supply;
• a plurality of boosting means including switching devices for boosting an output of rectifying means;
• smoothing means for smoothing outputs of the plurality of boosting means;
• a plurality of first voltage detecting means for detecting a voltage between main terminals of the respective switching devices of the plurality of boosting means;
• a plurality of selecting means for selecting only a voltage by which the switching device to be detected is in an on-state from respective voltages detected by the plurality of first voltage detecting means;
• a plurality of amplifying means for amplifying the respective voltages selected by the plurality of selecting means and outputting the voltages as current corresponding values corresponding to currents flowing in the switching devices;
• second voltage detecting means for detecting an output voltage of the smoothing means;
• and
• driving means which form pulse signals to the plurality of switching devices based on the current corresponding value and the output voltage, for driving the plurality of switching devices by the pulse signals.