The slope at the time of the ramp-up of the ramp signal Ramp11 generated by the ramp signal generating circuit 11 is smaller than that of the ramp signal Ramp3 generated by
the ramp signal generating circuit 3. If the ramp signal generating circuits are implemented by the configuration shoWn in FIG. 5A, these slopes can be set to desired values depending on the capacity of the capacitor Cx and a constant current provided to the capacitor Cx. Additionally, if the difference betWeen a supplied input voltage Vin and an output voltage to be kept is small, an inductor current moderately increases. Therefore, the slope of “control signa lam-current signal IL” is small. Accordingly, the timing at Which “ramp signal Ramp3+ramp signal Ramp11” becomes larger than “control signal lam-current signal IL” occurs immediately before the termination of the cycle of the ramp signal generating circuit 3. The reason Why the above described timing occurs immediately before the termination of the cycle Will be explained beloW.