A switching power supply device includes a switching transistor, a sense resistor, a transformer, an optocoupler, and a current limiting feedback circuit. The switching transistor is controlled to be turned on and turned off. The sense resistor is configured to generate a sense voltage when the switching transistor is turned-on. The transformer includes a primary winding to which an input voltage is applied when the switching transistor is turned-on, a secondary winding is configured to supply an output voltage to a load, and an auxiliary winding that is configured to detect the output voltage. The optocoupler is configured to generate first and second optocoupler currents corresponding to the output voltage. The current limiting feedback circuit is configured to generate first, second, and third feedback currents using a voltage of the auxiliary winding, the first, second, and third feedback currents being in inverse proportion to the output voltage.