A DC-DC converter prevents through current from flowing in an output transistor. A first transistor receives an input voltage. A second transistor is connected to the first transistor. A comparator is connected to the second transistor. The comparator detects current flowing through a choke coil based on the potential difference between two terminals of the second transistor to generate a switching control signal for turning the second transistor on and off. The second transistor and the comparator form an ideal diode. A control circuit of the DC-DC converter generates an activation signal for turning the first transistor on and off based on a pulse signal to keep an output voltage constant. A through current prevention pulse generation circuit generates a pulse signal for turning off the second transistor from before the first transistor is turned on to after the first transistor is turned on.