A switching power supply includes a switching element, a constant current element, a rectifying element, a first inductor, a second inductor, and a control circuit. If the switching element is on, the switching element supplies a power supply voltage to the first inductor and feeds an electric current. The constant current element turns off the switching element if the electric current of the switching element exceeds a predetermined upper limit. The rectifying element feeds the electric current of the first inductor if the switching element is turned off. The second inductor supplies the induced potential to a control terminal of the switching element. The control circuit supplies a pulse-like potential to a control terminal of the constant current element and outputs if an average of the potential is lower than a lower limit.