The invention includes a flip-flop circuit that controls a main switching element of a DC-DC converter by switching and an oscillation circuit that is connected to a set terminal of the flip-flop circuit and outputs an oscillation signal that gradually increases and decreases in oscillation frequency in accordance with an increase and decrease in output voltage value of the DC-DC converter when the DC-DC converter is in a transition state between a stop state and a steady operation state. In a process that the output voltage gradually rises and gradually falls, the oscillation frequency of the oscillation signal gradually rises and gradually falls, a time interval at which the main switching element is set into a conductive state is extended. No excess electric power is supplied to the output voltage, and the output voltage can be made to have a smooth ramp waveform.