To provide a low-cost DC-DC converter whose positive and negative output voltages can be surely controlled.

A switching element 12 is connected to one end of a primary winding 11 the other end of which is connected to a power source 10 and a serial circuit of a first diode 14a and first capacitor 15a is connected between the output side of a secondary winding 13 magnetically connected to the primary winding 11 and a grounding potential 16. In addition, a second diode 14b is connected between the connecting point A between the diode 154a and the capacitor 15a and the potential 16. In this state, the anode of the first diode 14a is connected to the capacitor 15a and the anode of a second diode 14b is connected to the potential 16. In addition, the constitution and connection for obtaining negative output voltages are the same as those for obtaining positive output voltages. Moreover, a feedback circuit is formed by connecting a control circuit 17 between the cathode of the first diode 14a and the base of the switching element 12.