A drive control circuit for a switching power supply device. The drive control circuit includes an output control circuit configured to generate an output control signal with a pulse width corresponding to an output voltage of the switching power supply device, a threshold setting circuit configured to determine a winding threshold voltage according to a direct current input voltage applied to the series resonant circuit formed of the leakage inductance of an isolation transformer and a capacitor of the switching power supply device, a winding detection circuit configured to compare a voltage generated in a tertiary winding of the isolation transformer with the winding threshold voltage and to accordingly output a winding detection signal, and a drive circuit configured to receive the winding detection signal and the output control signal, and to generate a pulse-width controlled drive signal for driving a first switching element of the switching power supply device.