A switching-control circuit configured to keep a transistor on for a predetermined time to generate a target-level-output-voltage from an input voltage. The circuit is configured to generate, every switching period of the transistor, a slope voltage corresponding to that of a ripple voltage contained in an output voltage during a time period when the transistor is off, limit an amplitude of the slope voltage so as not to exceed a predetermined amplitude greater than the amplitude of the slope voltage when the target-level-output-voltage is generated, add the slope voltage to a reference voltage, indicating a reference of the target-level-output-voltage, or a feedback voltage corresponding to the output voltage, and keep the transistor on for a predetermined time and thereafter turn off the transistor, when a level of either one voltage, added with the slope voltage, of the reference voltage and the feedback voltage reaches a level of another voltage thereof.