To provide a step-up DC-DC converter capable of reducing a ripple voltage of an output while achieving a desired output maximum current value without changing an external component.

A step-up DC-DC converter includes a switching element which flows current to an inductor, rectification means connected to an output side of the inductor, and a control circuit which controls on/off of the switching element on the basis of an output voltage and a voltage corresponding to an inductor current. The control circuit includes a first voltage comparison circuit which detects that the output voltage dropped to a prescribed electric potential, a second voltage comparison circuit which detects that the inductor current reached a prescribed current value, and a voltage generation circuit which generates a voltage inversely proportional to an input voltage. A voltage generated by the voltage generation circuit is supplied to the second voltage comparison circuit as a reference voltage. When the output voltage drops to the prescribed electric potential, the switching element is turned on. When the inductor current reaches the prescribed current value, the switching element is turned off.