A switching power source device is provided which comprises a drive controller 40 connected between an error amplifier 26 and changeover circuit 37. A second comparator 52 of drive controller 40 compares an output voltage or an equivalent signal thereto from error amplifier 26 with a numerical value from a sweep circuit 57 and produces an output to changeover circuit 37 to stop the on-operation of a switching element 4 and restrict an undesirable rise in output voltage during the light load period when the numerical value exceeds the output voltage or an equivalent signal thereto from error amplifier 26.