To provide a DC-DC converter adapted for a semiconductor integrated circuit without necessity of altering the circuit design for a different load condition.

The DC-DC converter comprises a coil L1 inputting at its one end a DC voltage Vin, a transistor Q1 connected at its other end to a collector, and a variable resistor circuit 104 connected at its one end to the emitter. The converter further comprises a rectifier circuit having a rectifier Di and a capacitor C1 connected in series between the collector of the transistor Q1 and the other end of the circuit 104 to supply the rectified DC voltage Vout to the output terminal, and a control circuit 101 inputting the output voltage Vout to supply a control signal to the base of the transistor Q1 and to control the voltage Vout a constant voltage. In the case of a light load, the resistance value of the circuit 104 is raised, while in the case of a heavy load, the resistance value of the circuit 104 is lowered.