The object of this invention is to improve efficiency in the step-up/down mode and eliminate ringing in the output voltage when switching between the step-up mode and the step-up/down mode. This DC-DC converter has a local feedback control pre-processing circuit 12 arranged between voltage input terminal IN and one of the terminals of choke coil 10 or node N.sub.x as well as an output feedback control booster circuit 14 arranged between the other terminal of choke coil 10 and the voltage output terminal OUT. Pre-processing circuit 12 has switching elements 16 and 18 and control circuit 20 that turns on/off switching elements 16 and 18 in a complementary manner. Control circuit 20 has error amplifier 22, reference voltage generating circuit 24, PWM comparator 26, inverter 28, and low-pass filter (LPF) 30.