A DC-DC converter having conversion efficiency that is not lowered by input voltage change. A mode control circuit of the DC-DC converter monitors the input voltage, output voltage generated from the input voltage, and output current. The output current changes in accordance with the output voltage. Based on the input voltage, output voltage, and consumption current of a controller of the DC-DC converter, the mode control circuit generates a signal that is in accordance with load current in which efficiency of a switching regulator and efficiency of a linear regulator are substantially the same. The mode control circuit further compares a signal corresponding to the output current and the signal that is in accordance with the load current to generate a mode control signal. The controller operates the DC-DC converter as the switching regulator or the linear regulator in accordance with the mode control signal.