A DC-DC converter includes a power conversion portion including a switching element; a first resistor having one terminal electrically connected to the power conversion portion; a second resistor having one terminal electrically connected to the other terminal of the first resistor; a third resistor having one terminal electrically connected to the other terminal of the first resistor; a constant current supply electrically connected to the other terminal of the third resistor; and a control circuit electrically connected to the other terminal of the third resistor and configured to control the switching element. Resistance R1 of the first resistor, resistance R2 of the second resistor, resistance R3 of the third resistor, a reference current Iref output from the constant current supply, and an output voltage Vout output from the power conversion portion satisfy a following formula: { ( 1 + R 3 R 2 ) · R 1 + R 3 } · I ref > - V out .