<p>There is provided a self-excited switching power supply circuit. A cycle control capacitor is charged with a flyback voltage generated in a feedback winding of a transformer during OFF operation period in which an exciting current does not flow in a primary winding of the transformer. An OFF control capacitor the charging speed of which changes ON operation period is charged with the charging voltage of the cycle control capacitor during the ON operation period in which an exciting current flows in the primary winding. The charging voltage of the cycle control capacitor is changed with a periodic cycle Tc sufficiently longer than an oscillation cycle To to make the oscillation cycle To of continuous oscillating operation variable based on the periodic cycle Tc. As a result, the frequency of a harmonic is distributed.</p>
