A DC-DC converter to convert DC power input from an external source into a predetermined DC power required for an electric load. A switch part in which each of a pair of switches that cuts or supplies the input DC power is connected in parallel with at least one other switch. A current sensor senses a load current flowing through the electric load and a controller controls the switch part to enable a number of the switches according to an intensity of the load current sensed by the current sensor. The enabled switches are driven by a PWM signal to cut or supply the input DC power to the load. By changing the number of enabled switches, unnecessary switching is prevented for lower load currents.