Abstract: A switching power source is capable of conducting constant-current drooping control on a load, increasing an energy conversion efficiency on a secondary side, and improving heat radiation performance. The switching power source detects whether or not an overcurrent exceeding a reference value V6 is passed to a switching element Q1, switches a first constant current I3 and a second constant current I4 smaller than the first constant current I3 from one to another according to a result of the overcurrent detection, directly superposes the first constant current I3 on a feedback voltage V3 at an input part, superposes the second constant current I4 on an output part where the feedback voltage is converted to have an impedance lower than that at the input part, and controls the ON-period of a pulse signal supplied to the switching element Q1 according to a resultant feedback voltage, thereby achieving constant-current drooping control on a load 29.