A DC-DC converter that suppresses increase in area and obtains high conversion efficiency irrespective of the output current. A controller controls a first output transistor and a second output transistor in a PWM operation mode or a linear operation mode based on output voltage of the DC-DC converter. The controller operates the DC-DC converter as a switching regulator that activates and inactivates the first output transistor and the second output transistor in a complementary manner during the PWM operation mode. The controller operates the DC-DC converter as a linear regulator that inactivates the second output transistor and controls the ON-resistance value of the first output transistor to perform linear operation with the first output transistor during the linear operation mode.